US President Joe Biden addresses striking members of the United Auto Workers (UAW) union at a picket line outside a General Motors Service Parts Operations plant in Belleville, Michigan, on September 26, 2023. (Jim Watson/AFP/Getty Images)

Washington (CNN) โ€” The United Auto Workers union on Wednesday endorsed President Joe Biden, a long-awaited announcement that is an important pickup for the president.

โ€œLook, I kept my commitment to be the most pro-union president ever,โ€ Biden said after receiving the UAWโ€™s endorsement at the groupโ€™s conference in Washington, DC, on Wednesday afternoon. โ€œIโ€™m proud you have my back. Let me just say Iโ€™m honored to have your back, and you have mine.โ€

The endorsement comes as the Biden campaign is making a full pivot to the general election, pointing to former President Donald Trumpโ€™s victory in the Republican primary in New Hampshire Tuesday as a clear sign that he is poised to emerge as the GOP presidential nominee.

The president and union leadership have long courted each other. Although itโ€™s a key endorsement for Biden, the backing from union leadership may not convince all of the rank-and-file to vote for the president in November. Biden won the endorsement of the UAW in the 2020 campaign, even though many rank-and-file members supported Trump.

Ahead of endorsing Biden, UAW President Shawn Fain said the choice union workers face in 2024 โ€œisnโ€™t about who you like. Itโ€™s not about your party. Itโ€™s not this bโ€”โ€”- about age. Itโ€™s not about anything, but our best shot at taking back power for the working class.โ€

He then referred to Trump using the worst insult that can be made in front of a room full of union workers.

โ€œDonald Trump is a scab,โ€ Fain said. โ€œDonald Trump is a billionaire, and thatโ€™s who he represents. โ€ฆ Donald Trump stands against everything we stand for as a union โ€“ as a society.โ€

The choice between Trump and Biden, Fain said, was clear.

โ€œJoe Biden bet on the American worker while Donald Trump blamed the American workers,โ€ he said. โ€œWe need to know whoโ€™s going to sit in the most powerful seat in the world and help us win as a united working class. So if our endorsement must be earned, Joe Biden has earned it.โ€

Trump has made appealing to union voters a key part of his political strategy, in no small part by targeting disaffected voters in parts of the Midwest who believe the Democratic Party has left them behind.

Biden, meanwhile, has continued to cast himself as the most pro-union leader. He joined members of the UAW in Michigan on the picket line last year in the middle of a strike โ€“ an unprecedented move for a sitting president.

The endorsement could be a factor in the battleground state of Michigan in November. Trump won the Great Lakes State in 2016 and Biden won it narrowly in 2020. The race is expected to be close again in November as Biden and the former president โ€“ should he win his partyโ€™s presidential nomination โ€“ both work to stake out their claim to be the champion of the working class.

The UAW had kept its powder dry on a potential endorsement, declining last year to join a cadre of high-profile unions in backing Bidenโ€™s reelection campaign ahead of high-stakes contract negotiations. At the time, the union cited concerns over Bidenโ€™s policies that would encourage a transition to electric vehicles.

The UAW has more than 400,000 members, and Biden โ€“ who has long relied on the political backing of unions โ€“ has touted its support in the past. The president has called American autoworkers โ€œthe most skilled autoworkers in the world.โ€ The groupโ€™s membership is mostly concentrated in Michigan, a presidential election battleground.

Fain previously warned this cycle that โ€œanother Donald Trump presidency would be a disaster.โ€

While Biden took care to show his support on the picket line, the administration lacked the legal or legislative authority to act as a participant in the negotiations, which ended in late October.

Rep. Dan Kildee, a Michigan Democrat, dismissed concerns Tuesday that Biden had not yet received the unionโ€™s endorsement.

โ€œNo, it doesnโ€™t,โ€ Kildee told CNNโ€™s Poppy Harlow when pressed on whether he was worried the endorsement had not yet been made.

โ€œThe UAW had other issues on its mind than injecting presidential politics into the 2023 challenges. They had an unprecedented strike. With the support of President Biden, they received an unprecedented contract. So, when I talk to auto workers, they understand that. And, you know, Iโ€™m very hopeful that organized labor generally, and the UAW specifically, will – will remember Joe Bidenโ€™s record and will stand with him as a result,โ€ Kildee added.

Trump has found support among the rank-and-file of the UAW despite Fainโ€™s strong criticisms and union leadershipโ€™s consistent support of Democratic candidates. On the same day that Biden visited a UAW picket line in Michigan, Trump spoke at a non-union auto shop in suburban Detroit โ€“ drawing the ire of the union.

Fain told CNN in December that he felt like the former president has never truly had the backs of UAW members.

โ€œYou go back to 2019, when he was a sitting president, and GM was on strike for, you know, 40 days. What did he say about the strikers in? What did he do to assist? What did you do show he cared about those workers, I mean, he was silent,โ€ Fain said.

โ€œYou go back to 2015, when he was running for the presidency. And he talked about, we need to do a rotation of all these good paying jobs in the Midwest somewhere else, not out of the country, but somewhere else in the country, and have these workers begging for their jobs back. You go back to the economic recession, and he jumped on โ€˜The bandwagon of the UAW is to blame for everything wrong with these companies.โ€™ And so those are facts, theyโ€™re indisputable.โ€