An unlikely alliance between a top Democrat, and a member of the conservative Freedom Caucus, has cast a trip line in front of the House’s “running start” on the appropriations process.

Last night, House Republicans delayed a vote on the first spending bill of the new session. The bill would have provided the funding for the Department of Veterans Affairs and military construction projects, and is usually the easiest appropriation to pass. A series of amendments from Rep. Chris Van Hollen (Md.) and Rep. Mick Mulvaney (R-S.C.), however, threatened to derail an agreement made by House and Senate negotiators to reconcile both chambers’ spending plans prior to a vote.

The amendments address a budgetary loophole involving the sequester (remember that whole thing?) and the Overseas Contingency Operations (OCO) fund. Mulvaney’s amendment seeks to block the Pentagon from using $532 billion from the OCO to fund overseas military construction projects at bases in Italy, Poland, Bahrain, Niger, Djibouti and Oman. Note: the OCO is not subject to the sequester caps passed in 2011. The budget the House was poised to pass would have appropriated $90 billion dollars from the OCO fund to the Pentagon; because that $90 billion comes from the OCO, it’s not subject to the sequester, either, even though the appropriations bill slapped another label on it.

More from The Hill:

Both Van Hollen and Mulvaney argued that using the war fund in such a way amounts to a budgetary “gimmick” to avoid spending caps established by the 2011 Budget Control Act (BCA).

“Let’s not go around the BCA. Let’s not use a slush fund or something that is off budget,” Mulvaney said during floor debate. “Let’s not be disingenuous.”

Van Hollen warned the anti-gimmick amendment could pass. With the amendment, the Military Construction-Veterans’ Affairs appropriations bill, which typically enjoys bipartisan support, could have difficulty passing.

“There is clearly bipartisan opposition to using the Overseas Contingency Operations budget as a slush fund for non-war related projects. I will continue to work with Congressman Mulvaney and my other colleagues to fight against this abuse of the budget process,” Van Hollen said in a statement.

He means it:

Mulvaney expressed displeasure at what he believes is the use of the OCO as a piggy bank backing non-war related projects:

“It spends $532 million in the OCO budget for matters that the Department of Defense admits are not war-related,” said Mulvaney, a two-term budget hawk who said last month he’d rather raise taxes than add to the deficit.

“These are matters that the Department of Defense included in its original base defense budget request, but which there isn’t enough money under the … caps,” he said during House floor debate earlier Wednesday. “The appropriators have taken those requests, which are admittedly not war-related, and buried it in this appropriations bill using the OCO money.”

Even without “slush fund” provisions like these, the House bill is expected to face opposition in the Senate, not only because of the renewed discussion over wasteful spending, but because McConnell and his team will need the help of six democrats to pass it.