Biden, making his final pitches to voters ahead of next Tuesday's races, is casting the midterms as a critical moment for the nation.
"I know there is a lot at stake in these midterm elections, from our economy, to the safety of our streets, to our personal freedoms, to the future of healthcare and Social Security and Medicare," Biden said this past week. "It's all important."
Republicans are favored to win back control of the House, according to FiveThirtyEight's midterm . As for Senate control, the shows a dead heat between Democrats and Republicans.
A Republican majority in either chamber would doom Democratic priorities like climate change, voting rights and abortion access. And the remaining pieces of Biden's signature "Build Back Better" framework would likely meet a similar fate.
"I think there were certainly pieces that got left on the table, like the child tax credit and the universal pre-K, that would be very hard to do in a divided Congress," Jim Kessler, the executive director at the center-left think tank Third Way, told ABC News.
Though Kessler had some optimism that bipartisan legislation could still get through a divided Congress, noting that many of Biden's major legislative achievements have gotten some Republican support: the CHIPS Act, the gun safety package and the infrastructure law.
"Biden is uniquely qualified to pass bipartisan legislation if that's necessary," he said. "He's done it before."
But other political strategists said a Republican majority could make governing difficult for Biden.
"The biggest challenge that both the president and the Democrats in Congress are going to face is going to be the extreme, dangerous Republican caucus," Craig Varoga, a Democratic strategist, told ABC News.
Republicans have expressed little interest in working with Democrats if they gain control on Capitol Hill.
GOP lawmakers are eying rollbacks of Biden's corporate tax increases, and Rep. Kevin McCarthy's vowed to repeal the $80 billion set aside for the Internal Revenue Service in the Inflation Reduction Act, which Republicans misleadingly claim will lead to more agents going after middle-class Americans. Also on the chopping block, McCarthy's said, is the steady stream of financial assistance to Ukraine as the nation staves off Russia's invasion.
And if Republicans take over the Senate, they could block Biden's judicial nominees, who need a majority vote to be confirmed.
Still, no legislation will get past the finish line without Biden's signature -- setting up potential showdowns between him and a Republican Congress.
Several House Republicans have already pledged to launch several investigations targeting the administration if they're the majority, including probes into Hunter Biden, the president's son. Hunter Biden, who also faces a federal probe over his tax affairs, has been scrutinized by the GOP for his international business dealings.
Other potential investigations would likely target COVID-19 policies, the withdrawal of troops from Afghanistan and the handling of the southern border. Some GOP lawmakers have already proposed impeaching Biden as well as Homeland Security Secretary Alejandro Mayorkas and Attorney General Merrick Garland.
"I’m already being told, if they win back the House and Senate, they’re going to impeach me," Biden told supporters last Thursday."I don’t know what the hell they’ll impeach me for."
What the midterms mean for 2024
Some Democratic candidates, especially those in tough races, have distanced themselves from the administration this cycle on hot-button issues like immigration or the economy. Others, such as Rep. Tim Ryan of Ohio and Rep. Dean Phillips of Minnesota, have openly suggested he shouldn't run for another term.
Biden himself has said he intends to run, but hasn't made any concrete announcements. At 79, and turning 80 later this month, he's currently the oldest person to serve as commander in chief in the nation's history.
One ABC News/Washington Post poll conducted in late September found that 56% of Democrats and independents that tend to vote for Democrats said they wanted "someone other than Biden" to run in the next presidential election.
If Democrats lose badly this cycle, it could potentially increase calls for Democrats to look elsewhere for a 2024 nominee.
"The stakes are obviously high but midterm elections that are bad for presidents are the norm, not the exception," Kessler said, noting several presidents -- most recently former President Bill Clinton and former President Barack Obama -- were able to win reelection after Democrats were trounced in the midterms.
Since the Civil War, the party in the White House has gained seats in the House just three times in 40 tries. In the Senate, since the direct election of senators began in 1914, they've gained or retained their seats just seven times.
If Democrats manage to hold onto their majorities in Congress, Kessler said it would be affirmation that "running a mainstream Democratic agenda through Congress works."