Dems’ Senate hopes are increasingly running through a single state. And it’s not looking great.

Control of the Senate increasingly appears to hinge on a single race, and it’s quickly moved in the wrong direction for Democrats: Sen. Jon Tester of Montana has fallen behind his opponent in poll after poll.

Democrats have been desperately pouring resources into helping Tester try to defy political gravity once again, with $45 million more slated for the final weeks of his battle with Republican Tim Sheehy.

As the situation in Montana has worsened, it’s raising uncomfortable questions for national Democrats trying to figure out how to hold the Senate: How far should they go to protect someone in a state Donald Trump won by 16 points in 2020? Should they mount a long-shot offense somewhere they haven’t been playing as much, like against Sens. Ted Cruz (R-Texas) or Rick Scott (R-Fla.)? Would some of that money be better spent shoring up the many other battleground seats they’re defending?

The answer, for now, is to stay the course. Democrats say there’s no meaningful discussion about diverting the tens of millions of dollars slated to help the third-term incumbent — and in some ways, they are boxed in.

“People really want to keep the Senate Democratic. But yeah, those are hard calls," said Sen. Tim Kaine (D-Va.), who stressed he would never bet against Tester.

For one thing, there are the optics of abandoning a sitting incumbent. And Tester himself has called it a “margin-of-error race,” echoing other Democrats who insist the race was always going to be close. But there are also no better options: Texas and Florida, the two uphill offensive opportunities that could offset a loss in Montana, are prohibitively expensive because of their size. It’s difficult to mount a serious statewide effort in either.

Meanwhile, Senate Democrats appear to be doing well in other battlegrounds, reducing the need for immediate and widespread triage. In many states, Democratic Senate candidates are running ahead of Vice President Kamala Harris — in some cases by significant margins. Even Sen. Sherrod Brown , who is considered to be among the most vulnerable Democrats, appears to be holding his own in Ohio.

So for Democrats, it’s Montana or bust. And while his colleagues are projecting confidence in his ability to win, Tester is clear-eyed about the challenge he faces.

“I do think polls do indicate things like, 'Well, you got more work to do.' But is it something that keeps me up at night?” Tester said in a Senate hallway last week. (No, he said — it doesn’t.)

Asked if “more work” meant spending, advertising or something else, he said: “More of everything.”

National Republicans wanted this race. They labored to secure the nomination for Sheehy, an aerospace executive and Navy veteran, and Senate GOP campaign chief Steve Daines personally intervened in his home state to snuff out a short-lived bid by Rep. Matt Rosendale .

Now they feel their work is starting to pay off. Recent polls have consistently shown Tester falling behind — one public survey showed Sheehy up 8 points — and Sen. Gary Peters (D-Mich.), the head of the Senate Democrats’ campaign arm, admitted Trump is likely to win the state by 20 points. Two independent prognosticators shifted the Senate race in the GOP's favor in recent weeks. And Montana Democrats lost an attempt to keep a Green Party candidate — who could draw votes from Tester — off the ballot.

The Democratic Senatorial Campaign Committee disputed the idea that their path to the majority was narrowing.

"Senate Democrats are strongly positioned to defend our majority and have multiple pathways to do so,” said David Bergstein, a spokesperson for the committee. “The most important factors in Montana — and in every other Senate race — are in Democrats' favor: We have the better candidate, the more effective message and the stronger campaign.”

And when asked about their colleague, Senate Democrats insisted Tester’s “earthy, direct” style, as Sen. Peter Welch (D-Vt.) put it, will propel him against the electoral headwinds. They all agreed that the party should continue to invest in Montana — and that Tester will have the money needed to win. Plus, the Montana ad market is nearing saturation, meaning Democrats can’t put more money onto the airwaves even if they wanted to.

“I don’t think it's going to be a resource issue,” said Welch. “It’s going to come down to just the mood of the country and Tester’s wonderful record of service.”

But all fall spending allocations carry some risks. Senate races will tighten in the final weeks, and races that look favorable now could quickly need more resources. And it will become harder to book time in Florida or Texas as rates rise in pricey markets like Miami, Houston and Dallas.

At some point, Democrats’ money in Montana will be hard to move elsewhere, even if they want to. In the meantime, they said, they’re keeping an eye on the two offensive reach states.

Peters told reporters Tuesday that Texas and Florida were “increasingly in play” — but did not commit to spending substantial resources in either.

“Decisions as to what kind of resources will go in are going to be made real time and are likely to evolve,” he said.

He conceded that a large media buy would likely be necessary to be viable in either state, but he also noted that traditional television has had “a smaller impact” thanks to other competing media sources, such as streaming or digital ads. Democrats could make strategic buys in those states, he said.

Digital ads, targeted cable, streaming and radio buys or field programs could help Rep. Colin Allred in Texas or former Rep. Debbie Mucarsel-Powell in Florida. Those can be far more cost-effective than the millions of dollars it would take to run TV ads, the price of which is rising by the day as the election nears.

“The segment of voters you need at the very end is a lot smaller. That's the good news,” Peters said. “The bad news is they're a lot harder to reach, and they're a lot harder to talk to, and you've got to be really smart on how you're focusing those resources.”

And Democrats have already begun some of those efforts. This week the DSCC announced a $25 million canvassing program that will reach 10 states, including Texas and Florida. And it also singled out the two states for digital advertising in its initial independent expenditure reservations. But no major TV reservations are slated.

Allred has raised eye-popping sums during his campaign and has placed some $37 million worth of ad buys from May through September, according to the media tracking firm AdImpact. Cruz has placed just $16 million, and a cohort of GOP super PACs have had to dump in money to try to make up the gap.

Even some Democrats eager to flip seats in Texas and Florida don’t want to sacrifice Montana to do it. Rep. Al Green (D-Texas) told POLITICO: “I'm not going to say transfer funds from Montana, but I will say that those who can spare it, it would seem to me that they would do what they can to help us.”

Republicans don’t believe Democrats will give up on Tester, either. National Republican Senatorial Committee spokesperson Mike Berg said in a statement, “We don’t expect national Democrats to leave swamp politician Jon Tester for dead.”

Both sides are expecting a grueling fight to the end. After all, control of the Senate is poised to come down to this.

“All of his races in Montana have been close. This one is going to be no different,” Sen. Tina Smith (D-Minn.), the DSCC vice chair, said of Tester. “This is what it's going to be like. It's going to be very tight until the very end.”