The “Stand with Su” effort is a direct counterweight to some of the forces that have been lobbying against her — including the name choice, as one of the main anti-confirmation groups is called “Stand Against Su.”

“Julie Su has been a champion for labor, and labor is mobilizing in the way only we can,” AFL-CIO spokesperson Ray Zaccaro said.

A key part of the pitch is that Su, who faces a committee vote Wednesday, is in the same mold as former Labor Secretary Marty Walsh, a seasoned politician who had fans on both sides of the aisle and who has been directly involved in rounding up support for her, according to an administration official. Su served as Walsh’s deputy secretary beginning in July 2021 and has been acting head of the department for the past month, after Walsh stepped down to run the NHL Players’ Association.

“She has worked hand in hand with Marty Walsh,” American Federation of Teachers President Randi Weingarten told POLITICO. “If you liked the way Marty Walsh operated as the Secretary of Labor, then there’s no reason not to embrace Julie Su.”

But Republicans say Su, who was labor secretary in California before coming to Washington, would veer sharply left of Walsh and used a confirmation hearing this week to portray her as anti-business and captive to labor’s priorities. Although all five of the senators in question voted to confirm Su as deputy secretary, Manchin, Tester and Sinema are likely to face tough reelection fights next year.

“The more that people learn about her track record and just how bad she was in this role in California, we’re seeing that shifting the debate,” Rep. Kevin Kiley (R-Calif.), a leading critic of Su, told POLITICO prior to her confirmation hearing. “It’s very different when you’re going for the top position than being under Marty Walsh.”

The battle over Su is the Biden administration’s first attempt at replacing a Cabinet secretary, and the latest test of Democratic leadership’s ability to confirm nominees after multiple high-profile misfires. Though Su is already steering the department, administrations are typically wary of issuing major policy decisions without a permanent leader, meaning that a protracted confirmation fight could bog down the agency for months.

Administration officials are holding nightly “war room” calls with Su’s backers to discuss the game plan for the following day and to track developments, according to a White House official. The administration also holds 15 to 20 check-in calls per day across labor and business groups.

Walsh has also been actively engaged in the process and advocating for Su with labor and business leaders and senators, according to an administration official.

Many Democrats on Capitol Hill are hopeful Kelly, Tester and King will support Su. If that is the case, and Sen. Dianne Feinstein remains in San Francisco recovering from shingles, Su and the White House would still need to win over Manchin and Sinema, both of whom have bucked the president in the past.

Neither senator is on the committee that will vote Wednesday on whether to advance Su’s nomination to the floor and attention will fully turn to them immediately after the vote.

Su has been ramping up her meetings with senators of both parties in recent weeks, though she has yet to meet with several key holdouts. She has spoken to Sinema, according to two sources familiar with the situation, and the White House is in touch with Manchin, an administration official said.

Su doesn’t have a traditional “sherpa,” a veteran lawmaker or some other plugged-in operative who typically leads Cabinet officials and other important nominees through the confirmation process on Capitol Hill. The lack of one has raised eyebrows among some of Su’s supporters about the White House’s level of support for the nomination.

The term “sherpa” is being phased out at the White House, however. Instead, she has a “navigator” — the senior leader of the Labor Department’s congressional affairs shop. The office has led Su through the process and accompanied her at each of her Senate meetings, according to that official.

Su is only the second Cabinet official to go through the confirmation process since the first months of the Biden administration — Office of Science and Technology Policy Director Arati Prabhakar being the other — and the agencies now lead the confirmation process, an administration official said.

With an obvious eye toward Manchin, the White House has heavily touted Su’s support from labor unions, including the AFL-CIO, Teamsters and, most significantly, United Mine Workers of America.

While a recent letter of support from Mine Workers President Cecil E. Roberts may pull weight with Manchin, Su supporters have been cautious to not be too heavy-handed with either him or Sinema, knowing that an overt lobbying effort may backfire.

“The White House knows what they need to do for the best outcome to get Julie Su confirmed,” said an organized labor official, who requested anonymity to discuss political strategy. “They know the relationship dynamics they have with the senators in question. And they know it’s a complicated circumstance that requires deft and delicate management.”

The White House’s light-touch strategy is not entirely reliant on unions to shoulder the lobbying load and the administration has highlighted her support from groups like the Los Angeles Chamber of Commerce, Small Business Majority and those representing Asian American and Pacific Islanders. If confirmed, Su would be Biden’s first AAPI Cabinet secretary and his fourth AAPI Cabinet member overall.

But organized labor is at the center of the pro-Su push.

“There’s a world of Julie Su supporters out there, and we’re trying to show that,” the labor official said. “We saw these senators vote for her [to become deputy secretary] and there’s no reason to vote against her now. It remains to be seen just how uncertain they actually are.”

— Daniella Diaz contributed to this report.