The good news for vulnerable Senate Republicans up to this point has been that, in the eyes of voters, they have more or less been able to separate themselves from their party's presidential nominee.

But keeping the toxic nominee at arm's length could get much more difficult for them in these final few weeks, for a reason that has nothing to do with Donald Trump: They are low on money at the worst possible time.

As Politico recently reported, the Senate Republicans' campaign arm has reserved $5 million for the last two weeks of the campaign, with no indication it is going to drop more cash this week, either. Senate Democrats' campaign arm has reserved $40 million for the last month.

Put another way, Senate Republicans are at risk of getting outspent 8 to 1 in the final stretch as they try to hold on to control of the chamber. (Outside groups are excluded in that calculation; we'll get to that later.)

The eyebrow-raising disparity in TV spending comes at exactly the wrong time for Republicans, for a few reasons:

1. Mid-October is the moment when voters finally started to tune into congressional races.

2. We're living in a post-2005-Trump-tape world, where a clear majority of voters are skeptical that Trump's apology was sincere and that his brags about sexual aggression were never translated into actions, according to a new Washington Post-ABC News poll. Translation: Trump is as toxic as ever, and no one's really sure how that's going to translate down the ballot.

3. To that point, newly released Senate Democratic polling in Senate battleground states suggests Republican candidates have few good options on Trump: Those who rescinded their support are viewed as doing it for political convenience, and 63 percent of respondents say Republicans should have done it months ago. (This polling should obviously be taken with a very large grain of salt, because it was commissioned by Senate Democrats. But it does corroborate our initial take on the Senate battlefield post-Trump tape: that rescinding their votes for Trump could backfire on Senate Republicans.)

4. Trump appears to have completely given up on running a traditional campaign. It feels as if every time he steps up to a microphone these days, it's to say something controversial: The election is rigged, the women accusing him of making unwanted sexual advances are not attractive enough, Hillary Clinton's health is a problem. Polls show that a majority of voters are turned off by that. If there were ever a time to push the “I'm not with Trump” message hard, now would be it — especially because at least five Senate Republican candidates have now said they are not voting for him.

Senate Republicans say they spent early and hard to try to distance their candidates from Trump. They were dealing with limited resources, so they made the strategic decision to put distance between Trump and their candidates in August and September, rather than try to make that case in late October. They have spent almost $30 million on TV ads this cycle (digital ads are a whole other calculation).

And again: So far, their strategy seemed to have been working. Despite all the heartache Trump has put them through, Senate Republicans in battleground states appeared to be outperforming their nominee before the hot-mic tape surfaced.

If Trump loses to Clinton by four or five points, there is evidence that Republicans in New Hampshire, Pennsylvania, Ohio and Florida can hang on anyway. That is because there is also evidence that voters just don't view Trump has a traditional politician, so Democrats' attempts to tie him to traditional politicians do not resonate. (Also, Clinton — trying to make a pitch palatable to Republican women — is not necessarily helping Democrats' cause by talking about Trump as if he were an anomaly in politics, almost unconnected to his party.)

“At the beginning of the cycle, if you would have outlined the scenario these candidates were facing, you would have said every candidate would have been down by 10,” said Josh Holmes, a Senate Republican strategist. “And somehow they've managed to stay basically where they have been all along.”

Senate Republicans have managed to stay afloat in the Year of Trump thanks in part to outside groups. Republicans have help from three Senate Republican groups — the Senate Leadership Fund, Granite State Solutions and One Nation. Politico reports that those groups have accounted for more than half of Republicans' TV spending in this cycle.

Senate Republicans hoped those groups would fill in the gap in the end of the cycle, too. But that may not happen.

When we talk about outside groups, Charles and David Koch come to mind. The billionaire brothers and their allied political groups are not supporting Trump but are spending on Senate races. They, too, spent early in states like Ohio. But as my colleague Matea Gold detailed in September, the Koch groups have moved away from TV ads to focus on a ground game in Senate GOP races.

Which is certainly helpful for Republicans in the raging battle for control of the Senate. As much as there is a TV gap favoring Democrats, there is a grass-roots gap as well, because Trump's campaign has all but forsaken it. Clinton's campaign, meanwhile, is in a position to expand the list of states and races it is playing in:

When it comes to TV, Senate Republicans appear to be in hope-and-pray mode. That sort of strategy does not exactly have a proven October record.