Rebel Senate Democrats are causing a political headache for President Biden ahead of 2024 by bucking their party and backing Republicans on contentious initiatives, including two in just the past week.

Two Democratic senators joined 48 Republicans on Wednesday to nullify the White House’s new 401(k) rule that allows retirement fund managers to consider the environment and social justice politics when weighing investments.

The rule “is just another example of how our administration prioritizes a liberal policy agenda over protecting and growing the retirement accounts of 150 million Americans that will be in jeopardy,” said West Virginia Sen. Joe Manchin III, one of the Democrats who voted to scrap the rule.

Joining Mr. Manchin in opposition was Sen. Jon Tester, Montana Democrat. Both men are vying for reelection in 2024 in states that former President Donald Trump won by double digits in 2020.

Despite bucking their parties, the rule is expected to remain intact, thanks to Mr. Biden‘s pledge to veto the legislation. Republicans are unlikely to muster the two-thirds votes necessary in both the House and Senate to override a veto.

The veto will be the first of Mr. Biden‘s presidency. It underscores the tenuous political environment the commander in chief and his party must traverse over the next two years.

While Democrats exceeded expectations in 2022 by expanding their control of the Senate to 51 seats, Republicans still won the House. And the new GOP majority is eager to use its power to put Mr. Biden and congressional Democrats on the defensive.

“Executive overreach has become synonymous with the Biden administration,” said Sen. Shelley Moore Capito, West Virginia Republican. “It’s created a desperate need for oversight from my Republican colleagues, both in the Senate and in the House of Representatives.”

The House Oversight Committee, for instance, is investigating not only the White House’s actions in the lead-up to the fall of Afghanistan, but also Hunter Biden‘s business dealings. The inquiries could have serious repercussions for Mr. Biden‘s expected reelection campaign in 2024, especially as Gallup already shows the president with a low approval rating, 42%.

Republican lawmakers are also using the privileged resolution process to fast-track messaging bills on issues popular with their voters. The tactic allows legislation to get a vote on the Senate floor via a simple majority and is not subject to the 60-vote filibuster threshold.

Republicans used the process to force a Senate vote on Mr. Biden‘s 401(k) rule.