President Biden has been unabashed about advancing his agenda, a boldness that is probably born both of his convincing win in the 2020 presidential election — at least in terms of the popular vote — and of his understanding that Republicans are unlikely to go out of their way to aid his presidency.

Note the difference here between “boldness in advancing an agenda” and “advancing a bold agenda.” While Biden’s out-of-the-gates efforts include components embraced by the more progressive members of his party, he has centered his initial policy pushes on proposals with broad public (not necessarily only Democratic) support.

But that boldness is almost entirely dependent on incredibly narrow majorities in Congress. At this point, after his party lost seats in 2020 and Biden himself plucked several sitting House members to work in his administration, the Democratic House majority is in the single digits. In the Senate, of course, it’s not even that; Republicans and Democrats hold the same number of seats, with controversial votes coming down to Vice President Harris’s ability to break ties.

Republicans are certainly not eager to make Biden’s life easier. Take Florida’s 20th Congressional District. It was represented by Alcee L. Hastings until his death this month. Replacing him in the heavily Democratic district requires a special election that Gov. Ron DeSantis (R) appears to be in no hurry to call. With the House as evenly divided as it is, Democrats can lose only two votes if they hope to pass legislation — a tricky proposition for Democratic leadership. Their majority in the 435-seat House is, as a percentage, only slightly wider than their majority in the Senate, even if you include Harris.

At the same time, 2022 is looming. If history is a guide, which it tends to be, the Democratic House majority will not survive the midterms.

Since 1970, there have been eight midterms that followed the inauguration of a new president. (We’re skipping Gerald Ford in that tally, given the unique circumstances of his ascent to the presidency.) Of those eight, the president’s party lost the national House popular vote in six elections. In seven, their party lost seats.

The useful exception to the rule here is 2002, when George W. Bush, buoyed by soaring popularity in the wake of the Sept. 11, 2001, terrorist attacks, enjoyed Republican House victories. Those things are connected: When presidential approval is higher, the president’s party tends to do better in midterm elections. You can see that pattern in the graph below, which uses Gallup polling data. Presidents’ parties tend to lose seats (farther to the left) when the president’s approval is lower (closer to the bottom). The three recent midterms in which the presidents’ party suffered the biggest losses were the wave elections of 1994, 2010 and 2018 — all years in which presidential approval was below 50 percent.

As of writing, Gallup has Biden at 54 percent approval. Exclude 1974 (that weird Ford year) from the mix, and the expected loss for a president’s party would be somewhere in the range of 10 seats. Given that each lost seat goes to the other party, that’s a 20-seat swing, more than enough to flip the House.

That’s also if Biden holds his approval at 54 percent, which may not be the pattern. Historically, presidents have honeymoon periods with the electorate, that gap between when a new president is still a blank slate and when he starts actually trying to pass policies. It’s not clear how much that still exists; Donald Trump never had much of a honeymoon because partisan sentiment about his presidency was firm from the outset. The same may hold true for Biden to some extent, though his sky-high approval from Democrats has essentially only one direction in which it can head.

If Biden loses the House, he essentially loses his ability to pass any legislation, regardless of how it might fare in the Senate. There, of course, his party’s grip is only slightly less shaky. As of writing, Cook Political Report has six Senate seats in the “toss-up” or lean category, meaning they are the most likely to swing between parties. Four are held by Republicans.

Biden and his party are obviously keenly aware of the window that exists. Senate Majority Leader Charles E. Schumer (D-N.Y.) got authorization from the Senate parliamentarian to allow his caucus to pass more bills without the 60-vote constraints of threatened filibusters. The president is pushing for a large infrastructure bill that would both meet a lot of Democratic policy initiatives and, he hopes, further bolster the sense among voters that he and his party are delivering on things they want.

The 118th Congress begins Jan. 3, 2023. That’s about 624 days from now. That, it is safe to assume, is how wide Biden’s window is. And that, it’s safe to assume, is a number that remains at the back of the minds of every Democratic leader in Washington.