House Republicans learned the same lesson early in Trump’s presidency when he rallied them to repeal Obamacare, then described their effort as “mean.”

As Trump reached the halfway mark of his term on Sunday, he has left a trail of negotiating partners from both chambers of Congress, both political parties and countries around the world feeling double-crossed and even lied to.

The result is that the president who campaigned as the world’s best deal-maker, vowing that he alone could fix Washington’s dysfunction, has been stymied as he looks for achievements before facing the voters again. Two years in, the man who built a political reputation as a guy who tells it like it is has lost the essential ingredients to closing deals: credibility and trust.

“He just undermined the trust and confidence that some Republican members did want to have in him,” said Carlos Curbelo, a Florida Republican who lost his House seat in November, in part because of Trump’s unpopularity.

The president’s squandered credibility, overlaid with nonstop investigations, is likely to imperil a second-half agenda that includes basic responsibilities — raising the nation’s borrowing limit, most essentially — as well as more ambitious goals. Among those are measures to rebuild the nation’s infrastructure, win congressional approval of a revised trade deal with Mexico and Canada, overhaul immigration laws and lower the costs of prescription drugs.

Trump’s trust deficit was a factor Saturday in Democrats’ quick dismissal of his proposed compromise to end the shutdown, an offer of temporary relief for some immigrants and refugees — relief from deportation threats that stem from his policies — in return for his wall money.

McConnell, having been burned, has largely left the shutdown fight to Trump. House Republicans, having lost their majority in large part because of voters’ own dismay with Trump, are now on the sidelines as he must battle House Speaker Nancy Pelosi. And Democrats, following her lead, are emboldened given their experience with the president’s unreliability as a negotiating partner.

Trump’s tactics were honed over decades. Throughout his business career, he moved from one project to the next — real estate development, sales, casinos and branding — often leaving scorned partners or creditors to deal with the fallout from bankruptcies or deals gone bad.

“This was all to stay ahead of his reputation,” said Michael D’Antonio, author of “The Truth About Trump.” But “in Washington,” he said, “you can’t escape who you are for very long. He’s proven that he can’t keep his word.”

The president has broken records for false statements, according to nonpartisan fact checkers. An increasing majority of voters — by 61% to 34% in one recent poll — say he is not honest. The same poll, from Quinnipiac University, found that voters also rated his leadership skills as poor, by 58% to 39%.

Complicating the problem, Trump has churned through staff faster than his predecessors. He has surrounded himself with a collection of temporary officials, family members and inexperienced advisors with little sway on Capitol Hill.

“They’re lacking some of the usual negotiating infrastructure,” said John Lawrence, former chief of staff to Pelosi. “In this White House, everything changes the next day: the personnel, the policies, the view of reality.”

Republican lawmakers’ criticism is muted, however, because even as Trump has ranked among the least popular presidents in modern history, he has consistently commanded overwhelming support from Republican voters, according to polls.

Still, the mistrust from nearly every quarter of Congress has grown each time he has broken his word, complicating efforts to pass his initiatives, according to former lawmakers, aides and close observers.

“Even things that should on paper be easy, there just always seems to be a way for him to step on his own foot,” said a former aide who requested anonymity to avoid upsetting his current employer. “Sometimes, this is unintentional — he just says stuff.”

The act that precipitated the month-old shutdown, and has come to define it, occurred in December. McConnell received bogus assurances from the White House that Trump would sign a Senate bill to fund and keep the government open to Feb. 8 while negotiations on border money proceeded, according to a person familiar with the discussions.

After senators approved the bill by a voice vote, Trump, egged on by conservative media personalities, rejected the legislation in favor of a fight with Democrats over the wall. Without any bill funding a quarter of the government, a partial shutdown began days later.

McConnell, Republicans’ foremost deal-maker, has since stayed in the background. Other Republican senators were left vulnerable to conservatives’ charges they were too quick to cave, even as they were stuck answering for the government services unfulfilled and hundreds of thousands of federal employees unpaid, with no sense of how the president intended to win.

“It would have been great if they had told us they wanted this fight, because we would have started working on it,” Florida Republican Sen. Marco Rubio fumed as the shutdown began, three days before Christmas. “We have to deal with it now.”

Lawmakers have been dealing with Trump’s abrupt tactical shifts from his start, and at the White House he leaves the impression with each advisor who talks with him that he shares their point of view, until he doesn’t.

“Sonny Perdue’s right on that. Oh, no — Mick Mulvaney’s right on that,” said one former official, imitating Trump talking about two Cabinet members. The official added, “You sort of feel like you’re a little bit of a pinball.”

After Trump seems to have made a decision, he remains “flexible,” as another former aide put it, making it nearly impossible for his staff to craft a strategy to rally Congress or the public. Often, he will hear from far-right lawmakers in the House Freedom Caucus, or from like-minded commentators including Ann Coulter, Laura Ingraham or Sean Hannity.

That tendency first became clear in 2017 when Trump initially celebrated, and then denigrated, House Republicans’ vote to repeal President Obama’s Affordable Care Act.

“The ‘mean’ comment and some other things really pulled the rug out from under” House Republicans, said Matt Gorman, a former communications advisor to them.

Stephen K. Bannon, Trump’s former chief strategist, implicitly acknowledged the president’s weakness as a legislative deal-maker, arguing that he has been able to fulfill promises where he hasn’t needed Congress’ approval, including on challenging China over trade.

Echoing some other Trump allies, Bannon argued that Trump, lacking governing experience, “put his trust in” McConnell and former House Speaker Paul D. Ryan to pass his legislative agenda, only to be often disappointed. Trump and his advisors naively believed he could win healthcare, tax and infrastructure legislation in the first year, Bannon said, yet he got only the tax cuts bill, which Trump largely outsourced to Congress.

In Congress, scars from the healthcare debacle have lingered, undermining Trump’s influence. Lawmakers are often skeptical when Republican leaders and White House aides lobby them for his bills, according to former aides and lawmakers, demanding to know where the president really stands.

Often, the Trump allies can’t answer unequivocally.

“We know he’s new at this,” lawmakers would tell Trump advisors, according to Marc Short, former White House director of legislative affairs. But, they’d add, “We can’t go back and take tough votes if he’s going to call our bill ‘mean.’”

That sentiment was cemented in March last year, as Congress debated another government-funding bill. Then, too, immigration was the issue that set Trump off.

For weeks, his administration supported the $1.3-trillion spending bill, saying it wasn’t perfect but would bolster the military, enhance immigration enforcement and keep the government open. Officials had a plan to sell it to the public, enlisting the Defense secretary at the time, James N. Mattis, to highlight pay raises for soldiers and money for new equipment.

But as a bill-signing ceremony approached, Trump “just got madder and madder” — riled by hard-right lawmakers and conservative media figures who complained that the legislation didn’t fund a border wall, a former official recounted. Trump tweeted angrily, threatening a veto.

Ultimately, Trump signed the bill, but only after calling the measure “ridiculous” and insisting, “I will never sign another bill like this again.” Even those who had given Trump a pass on earlier betrayals walked away angry.

“What kind of credibility do you have when the president says he supports a bill and then says he doesn’t like it anymore?” one of the former officials asked.

Curbelo, who represented a heavily Latino district in South Florida, was an early Trump skeptic. Even so, in June he and a group of California Republicans were counting on the president to follow through on earlier promises and support legislation providing a path to citizenship for hundreds of thousands of immigrants who years ago came to the country illegally as children.

The lawmakers had devoted nights and weekends to the compromise effort, along with House Republican leaders and some hard-line immigration hawks. Many conservatives opposed the bill, despite provisions to reduce legal immigration and provide nearly $25 billion over a decade for border security, much of it for Trump’s desired wall.

Curbelo and others believed that with Trump’s support, the measure could pass in the House and keep negotiations alive in the Senate. They also thought passage might give moderate Republicans like him and the Californians a fighting chance to keep their House seats in districts with Latino voters.

Yet when Trump showed up for a pep talk to House Republicans, he barely mentioned the bill. Instead he ranted about Hillary Clinton, the 2016 election and the Russia investigation. He insulted a popular congressman, Rep. Mark Sanford of South Carolina, who had just lost a Republican primary after clashing with Trump.

There were boos, confused faces and murmurs of incredulity. Curbelo said he considered asking Trump about the bill, subtly reminding him why he was there. But a bell summoned lawmakers to the House floor for a vote.

Trump tweeted afterward, insisting he supported the bill but predicting doom in the Senate. With so little backing from the president, the immigration bill fell, 121 to 301.

Curbelo, along with one of the other negotiators, Rep. Jeff Denham of Turlock, lost their reelection bids in November. Republicans overall lost a net 40 seats and control of the House.

“He would have had by far one of the biggest wins of his presidency had he been helpful,” Curbelo said.

Times staff writers Eli Stokols and Jennifer Haberkorn contributed to this report.

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