WASHINGTON —  Republicans have won enough seats to control the U.S. House, completing the party’s sweep into power and securing their hold on government alongside President-elect Donald Trump.

A House Republican victory in Arizona, alongside a win in slow-counting California earlier Wednesday, gave the GOP the 218 House victories that make up the majority. Republicans earlier gained control of the Senate from Democrats.

With hard-fought yet thin majorities, Republican leaders are envisioning a mandate to upend the federal government and swiftly implement Trump’s vision for the country.

The incoming president has promised to carry out the country’s largest-ever deportation operation, extend tax breaks, punish his political enemies, seize control of the federal government’s most powerful tools and reshape the U.S. economy. The GOP election victories ensure that Congress will be on board for that agenda, and Democrats will be almost powerless to check it.

When Trump was elected president in 2016, Republicans also swept Congress, but he still encountered Republican leaders resistant to his policy ideas, as well as a Supreme Court with a liberal majority. Not this time.

When he returns to the White House, Trump will be working with a Republican Party that has been transformed by his “Make America Great Again” movement and a Supreme Court dominated by conservative justices, including three whom he appointed.

Trump rallied House Republicans at a Capitol Hill hotel Wednesday morning, marking his first return to Washington since the election.

“I suspect I won’t be running again unless you say, ‘He’s good, we got to figure something else,’” Trump said to the room full of lawmakers, who laughed in response.

House Speaker Mike Johnson, who with Trump’s endorsement won the Republican Caucus’ nomination to stay on as speaker next year, has talked of taking a “blowtorch” to the federal government and its programs, eyeing ways to overhaul even popular programs championed by Democrats in recent years. The Louisiana Republican, an ardent conservative, has pulled the House Republican Caucus closer to Trump during the campaign season as they prepare what he called an “ambitious” 100-day agenda.

“Republicans in the House and Senate have a mandate,” Johnson said this week. “The American people want us to implement and deliver that ‘America First’ agenda.”

Trump’s allies in the House are already signaling they will seek retribution for the legal troubles Trump faced while out of office. The incoming president Wednesday said he would nominate Rep. Matt Gaetz (R-Fla.), a fierce loyalist, for attorney general.

Meanwhile, Rep. Jim Jordan (R-Ohio), the chair of the powerful House Judiciary Committee, has said GOP lawmakers are “not taking anything off the table” in their plans to investigate special counsel Jack Smith, even as Smith is winding down two federal felony indictments of Trump that charge him with crimes related to his attempts to overturn his 2020 election defeat and illegally hoarding classified documents at his Mar-a-Lago estate.

Still, with a few races still uncalled, the Republicans may hold the House majority by just a few seats as the new Congress begins. Trump’s decision to pull members from the House for posts in his administration — Reps. Gaetz, Mike Waltz and Elise Stefanik so far — could complicate Johnson’s ability to maintain a majority in the early days of the new Congress.

Gaetz submitted his resignation Wednesday, effective immediately. Johnson said he hoped the seat could be filled by the time the new Congress convenes Jan. 3. Replacements for members of the House require special elections, and the congressional districts held by the three departing members have been held by Republicans for years.

With the thin majority, a highly functioning House is also far from guaranteed. The last two years of Republican House control were defined by infighting as hard-line conservative factions sought to gain influence and power by defying their party leadership. While Johnson — at times with Trump’s help — largely tamed open rebellions against his leadership, the right wing of the party is ascendant and ambitious on the heels of Trump’s election victory.

The Republican majority also depends on a small group of lawmakers who won tough elections by running as moderates. It remains to be seen whether they will stay onboard for some of the most extreme proposals championed by Trump and his allies.

House Democratic leader Hakeem Jeffries, meanwhile, is trying to keep Democrats relevant to any legislation that passes Congress, an effort that will depend on Democratic leaders unifying more than 200 members, even as the party undergoes a postmortem of its election losses.

In the Senate, GOP leaders, fresh off winning a convincing majority, are already working with Trump to confirm his Cabinet picks. Sen. John Thune of South Dakota won an internal election Wednesday to replace Sen. Mitch McConnell, the longest-serving party leader in Senate history.

Thune in the past has been critical of Trump, but he praised the incoming president during his leadership election bid.

“This Republican team is united. We are on one team,” Thune said. “We are excited to reclaim the majority and to get to work with our colleagues in the House to enact President Trump’s agenda.”

The GOP’s Senate majority of 53 seats also ensures that Republicans will have breathing room when it comes to confirming Cabinet posts, or Supreme Court justices if there are vacancies. Not all those confirmations are guaranteed. Republicans were incredulous Wednesday when the news hit Capitol Hill that Trump would nominate Gaetz as his attorney general. Even close Trump allies in the Senate distanced themselves from supporting Gaetz, who had been facing a House Ethics Committee investigation into allegations of sexual misconduct and illicit drug use.

Still, Trump on Sunday demanded that any Republican leader must allow him to make administration appointments without a vote while the Senate is in recess. Such a move would be a notable shift in power away from the Senate, yet all the leadership contenders quickly agreed to the idea. Democrats could potentially fight such a maneuver.

Meanwhile, Trump’s social media supporters, including Elon Musk, the world’s richest person, clamored against picking a traditional Republican to lead the Senate chamber. Thune worked as a top lieutenant to McConnell, who once called the former president a “despicable human being” in his private notes.

However, McConnell made it clear that on Capitol Hill the days of Republican resistance to Trump are over.

Groves and Mascaro write for the Associated Press.