GOP Senate control cements a conservative court for a generation.

The stakes for Democrats in their extraordinary public schism over whether President Joe Biden should withdraw from the 2024 presidential race extend far beyond the White House. A decisive loss at the top of the ticket could cost Democrats control of the US Senate for the remainder of this decade and cement Republican dominance of the Supreme Court for a generation. So far, Democratic anxiety about the presidential race’s impact on the Senate has been muted because public polling has almost invariably shown their candidates still leading in the key states where Biden has fallen behind former President Donald Trump. But recent history raises deep questions about whether Democratic Senate candidates can continue to levitate as far above the presidential ticket as polls now show. Throughout this century, but especially over roughly the past decade, it has grown increasingly difficult for Senate candidates in either party to win in states that usually vote for the other side in presidential contests. During the 2016 and 2020 election years, Republican Sen. Susan Collins of Maine was the only candidate, out of 69 total Senate races, who won in a state that voted the other way at the presidential level. This year, Democrats are defending an unusually large concentration of Senate seats in states that now appear at risk for them in the presidential contest. If Democrats lose a substantial number of those seats this year, it could be very difficult for them to recapture a Senate majority before these same seats come up again in 2030. The reason is that very few of the other Senate seats Republicans now hold are in states where Democrats have a realistic chance of winning, absent a dramatic change in their political balance. In turn, extended GOP control of the Senate, coupled with a return of Trump to the White House, would give the party ample time to nominate and confirm much younger replacements for Samuel Alito (74) and Clarence Thomas (76), the two oldest and most conservative Supreme Court Justices, and possibly also Sonia Sotomayor (70), the oldest Democratic-appointed justice.

“Because of the big sorting out of the states … Democrats have a narrower path to a Senate majority than Republicans do, which means this year is crucial,” said former Democratic Sen. Evan Bayh of Indiana. “The margin of error [for Democrats] is not high, and the consequences will be with us for another six years.” If the presidential and Senate elections go badly for Democrats, Bayh added, Republicans “could change the judicial branch of government for a generation.” Vulnerable Democratic Senate seats this year fall into three broad buckets. The first includes three states that Trump carried in 2016 and 2020 and that he is virtually certain to win again — likely by a substantial margin. In that group, both sides concede the GOP will win the West Virginia seat being vacated by retiring Sen. Joe Manchin, who’s now an independent but still caucuses with Democrats; veteran Democratic Sens. Sherrod Brown of Ohio and Jon Tester of Montana, who have survived difficult reelections even as their states have moved right, are facing substantial challenges this year. If Republicans win just two of those three states, they would still seize control of the Senate (absent offsetting Democratic wins in any GOP-held seats, which are unlikely). But if Democrats only lost some combination of the three 2020 Trump states, they would remain close enough to the GOP in the chamber to retain realistic hopes of recapturing the Senate in 2026 or 2028. The real risk to Democrats is that their losses could extend beyond that inner circle of strongly red-leaning states — particularly if the presidential race goes badly. Democrats are defending five more Senate seats this year in presidential swing states where most polls now show Biden trailing, or at best running even. That list includes Democratic Sens. Bob Casey in Pennsylvania, Tammy Baldwin in Wisconsin and Jacky Rosen in Nevada, as well as Reps. Elissa Slotkin and Ruben Gallego, who are seeking open Senate seats now held by Democrats in Michigan and Arizona respectively. (Retiring Sen. Kyrsten Sinema of Arizona still caucuses with Democrats after becoming an independent.) Biden’s 2020 margin of victory was three points or less in all of those states.

As Biden’s position has weakened since last month’s CNN debate, strategists in both parties are just beginning to look at another circle of Democratic-held Senate seats in more strongly blue-leaning states where some polls have suggested an unexpectedly competitive presidential race. Topping that list are the contests in New Mexico, where Democratic Sen. Martin Heinrich is facing Nella Domenici, the daughter of the late Pete Domenici, a long-time Republican senator from the state; and New Jersey, where Republicans chose a relatively centrist nominee, Curtis Bashaw, to oppose Democratic Rep. Andy Kim in a race complicated by the possible independent candidacy of indicted Democratic Sen. Bob Menendez. Even if the Democrats’ vulnerability ultimately does not extend to that outer perimeter, significant losses for the party in the first two circles, as I’ve written, could leave them with few paths back to a Senate majority for the remainder of this decade.