There’s increasing nervousness on Capitol Hill these days about the one thing that has to be done on the budget before voters go to the polls.

Unlike 2011, when multiple spending, tax and debt ceiling deadlines were repeatedly met only through last-minute deals that had those both inside the Beltway and on Wall Street biting their nails, there is only one must-be-passed-by date before November’s elections: Oct. 1, when fiscal 2013 begins and funding to keep the federal government operating must be enacted to avoid a shutdown.

Until very recently that date wasn’t considered to be much of an issue. The thinking was that, after the way the GOP took it on the chin politically after the 1995 and 1996 shutdowns and after the drop in Congress’ approval rating after last year’s fight over raising the debt ceiling, House Republicans wouldn’t dare prevent a continuing resolution from being adopted just a month before the elections. They might huff and puff, but blowing the House down and in the process reminding voters only weeks before they go to the polls how unhappy they were last August wasn’t thought of as an especially smart — and, therefore, likely — strategy.

That prevailing opinion has begun to change as the political realities of the CR fight become clearer. In particular, there are growing doubts about the House GOP leadership’s ability to control the situation.

Remember that, despite having a majority, House Republicans weren’t able to pass the 2011 continuing resolution without Democratic votes. Only 182 of the 241 Republicans voted in favor of the conference report.

The question in 2012 is whether Democrats will be willing to supply the votes again if Republicans can’t get to a majority on their own.

This is of growing concern because the only CR that might be acceptable to that many House Republicans is likely to have a spending level that House Democrats won’t agree to. It’s also not likely to be agreeable to House Democrats if, as some suspect, the House GOP-preferred CR includes a provision that cancels the military spending part of the Jan. 2 sequester that was triggered when the anything-but-super committee failed last November to come up with a deficit reduction plan.

The differences between the spending levels that would be acceptable to each party are substantial and, even though there’s a number between the two that in a previous era might have been an obvious way to deal with the situation, the split-the-difference compromise probably isn’t possible in the current political environment.

Democrats appear to be ready to fight to the death for the $1.047 trillion (sorry, but rounding to three decimal places is important here) discretionary spending level agreed to in the Budget Control Act, most of the tea party wing of the House GOP seems just as adamant that the number should be $1.028 trillion, and a subset of the tea party wing has been pushing for $937 billion.

At least for the moment, neither of the lower spending levels nor the sequester change are acceptable to Senate Democrats, who are virtually certain to insist on the BCA-approved amount and that the sequester not be changed.

There are also increasing doubts about Speaker John Boehner’s (R-Ohio) ability — or willingness — to push his caucus to accept a spending level higher than the tea party wants in order to avoid a confrontation with the Senate and risking a shutdown.

Even if he were willing, it’s also not at all clear that enough House Republicans would vote with Boehner if he wanted to raise the spending level to deal with the Senate’s objections. In other words, pushing for an agreement with the Senate could cost the Speaker GOP votes in the House and he would have no guarantee that House Democrats would go along, as they did in 2011.

It could also cost Boehner his speakership. As his exceptionally hard-line speech from several months ago about not raising the debt ceiling again without dollar-for-dollar spending cuts — a tea party basic tenet if there ever was one — made clear, Boehner apparently feels as if he still has to prove his credentials to this group or live in fear of being challenged for Speaker next year.

That puts Boehner in a very tough political box. Compromising with the Senate might get a CR passed and avoid the government shutdown that could be devastating for Republicans on Election Day, but it might well put his speakership in serious jeopardy. Not compromising would reaffirm his tea-party-preferred street cred on spending but could precipitate the shutdown that, if the past is any guide, could cost his Members dearly on Election Day.

And, knowing all this, it’s hard to see how House Democrats will make it easier for Boehner by again agreeing to supply the votes to pass a CR.

In the past, this situation might have been avoidable by everyone agreeing to a short-term (as in six weeks or so) CR with a higher spending level than the tea party wants but with a Boehner assurance that the next CR will be at or below the GOP-preferred limit. But with many tea party folks feeling that many of last year’s spending-related promises by the leadership weren’t delivered, that type of deal might not be possible this time.

Stan Collender is a partner at Qorvis Communications and founder of the blog Capital Gains and Games. He is also the author of “The Guide to the Federal Budget.”