But while the topline budget numbers set by the budget deal go through October 2015, the funding passed in January expires at the end of next month, on September 30. Both houses must pass new funding bills—likely in the form of a continuing resolution—to keep the government running. And that has raised the possibility of further shenanigans.

A well-placed House Republican source tells me GOP leadership is increasingly nervous about the potential for a rebellion on the funding bill. The small but influential hard core of House conservatives were emboldened by what happened earlier this month with the border bill: A proposal favored by Speaker John Boehner to address the border crisis with emergency funding and expedited deportations had to be pulled when conservatives, egged on by Senator Ted Cruz, revolted. The legislation the House passed instead had a smaller price tag and would bar President Obama from continuing his policy of allowing some young undocumented immigrants to stay in the U.S. The Democrat-led Senate, meanwhile, did not manage to pass its own version of border legislation at all, so Congress failed to act on the issue.

House conservatives like Michele Bachmann and Steve King considered the episode a major victory. Bachmann called it a highlight of her career. Now, Republican leaders are worried that conservatives will not go along with a simple government-funding bill unless it reflects their priorities.

One possibility, raised by Senator Marco Rubio in an interview with Breitbart this week, is attaching to the funding bill a mechanism to stop Obama from taking executive action to liberalize immigration enforcement, as he has already done and threatens to do further. "There will have to be some sort of a budget vote or a continuing-resolution vote, so I assume there will be some sort of a vote on this," he told the publication. "I'm interested to see what kinds of ideas my colleagues have about using funding mechanisms to address this issue." Making government funding contingent on immigration-related legislation would instantly turn it into a highly charged partisan battle.

Another possibility is that reauthorization of the Export-Import Bank would be attached to the continuing resolution, either by Senate Democrats or by House Republican leadership. The formerly obscure lending fund has drawn the ire of the grassroots left and right, but mostly right, which charges that it constitutes a cronyistic corporate-welfare scheme. The bank's authorization runs out on September 30, the same day the federal government funding is set to expire. Business groups are lobbying hard for its renewal, but opposition has now gained momentum among conservatives: At this month's meeting of the Republican National Committee, a resolution opposing the bank was only narrowly defeated by the committee's members, 67 votes to 63. House conservatives might well refuse to agree to a government-funding bill that also reauthorizes the bank.