Detroit, Michigan - Joe Biden made history this week by becoming the first sitting president to visit a picket line, but several of his 2024 challengers are demanding the president do more to protect workers from greedy bosses.

President Joe Biden donned a United Auto Workers (UAW) baseball cap and traveled to Detroit on Tuesday to express his support for the union's Stand Up strike against the Big Three carmakers: Ford, General Motors, and Stellantis.

Though the president's action was historic, his political challengers from the left say it is not enough to guarantee the basic rights and dignity of striking workers.

Speaking from a UAW picket line, Independent presidential candidate Cornel West said, "I can't stand bosses. I can't stand profit-obsessed owners that treat workers as if they're less than human."

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"I know the president was here yesterday, and symbolic gestures, you know, they're empty if you don't follow through," West continued. "He broke the back of railway workers' strikes. Already he's been rationalizing corporate greed for the last 35 years. So, it's nice for him to come and say some words and things, but we need more than pretty words."

"You've got to follow through because we're talking about issues of life and death. We're talking about issues of dignity. And we're talking about issues of benefits and wages because the workers have been ripped off."

Claudia De la Cruz, presidential candidate for the Party for Socialism and Liberation, also called out Biden's appearance as mere lip service, referring to the president's picket-line visit as "minimal effort and mediocre."

"It would make more sense to create a society where workers have control of what they produce and dignified working conditions," she wrote on X.

While the top third-party and Independent candidates have gone all-in on autoworkers' fight for fair wages and working conditions, Biden's 2024 rivals in the Democratic Party primary have also shown support for the UAW.

Progressive candidate Marianne Williamson backed the strike with her own visit to the Detroit picket line on Wednesday.

"My father was a labor organizer with the CIO in Detroit in the 1930s. My brother worked for Cesar Chavez in the late 1960s. My parents always said, 'If you cross a picket line don't bother to come home,'" Williamson posted on X.

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"From WGA and SAG to Amazon to Starbucks to the UAW, organized labor hasn't exerted this much power for decades. It's a long overdue repudiation of institutionalized economic injustice, worthy of all our support. Labor's win is everyone's win, because a more fair society benefits all," she added.

Meanwhile, Robert F. Kennedy Jr. has stood with autoworkers in Swartz Creek, Michigan, and said in a statement, "I'm not visiting the picket line for a photo op. I am taking this opportunity to affirm the importance of organized labor to make American capitalism function fairly. I will stand four-square with working men and women in defense of their economic rights and intend to make the White House America's Local Number 1."

Republican frontrunner Donald Trump on Wednesday skipped out on the second GOP primary debate to speak at a non-unionized auto supplies factory in Michigan calling for UAW leaders' endorsement.