Congressional Democrats have yet another thing to worry about going into this year's midterm elections.

A temporary pandemic relief program aimed at lowering healthcare premiums under the Affordable Care Act (ACA), also known as Obamacare, is set to expire unless Democrats can revive a reconciliation bill that extends the financial assistance past the end of the year. And that means striking a deal with Sen. Joe Manchin (D-WV).

If they can't, roughly 13 million Americans will be hit with steep price hikes amid crippling inflation, in what Insider describes as a "time-bomb."

"There's no denying that if they are not extended, then there could definitely be a political impact," said healthcare policy analyst Charles Gaba.

Voters are set to receive notices about premium increases in late October, as they head to the ballot box for the November midterms. Others would find out during the ACA open enrollment period, which begins on November 1.

"If Congress lets the ACA premium help in the American Rescue Plan expire at the end of this year, middle-class people buying their own insurance would be hit hardest," tweeted Larry Levitt, vice president for health policy at the Kaiser Family Foundation.