DETROIT — President Joe Biden on Tuesday became the first sitting president to walk a picket line with striking workers, vividly demonstrating his commitment to labor and its central role in his reelection campaign.

Biden’s choice to show solidarity with striking auto workers at a time of great promise and peril for the labor movement represented a tectonic shift for an office historically known for breaking strikes, not supporting them.

The move also appeared to be a clear counter to Donald Trump, who plans to visit Michigan on Wednesday instead of participating in the second Republican primary debate — the latest sign that both candidates have moved beyond the primary phase of the election and are focused on November 2024.