A rebel faction of right-wing Republicans has, so far, held up negotiations in the House, the lower congressional chamber, with a demand for significant cuts in spending, including a call for no more US funding of the war in Ukraine.
Receiving vocal support online from former President Donald Trump, the hard-liners have tanked efforts by Mr McCarthy to shepherd legislation needed to break the impasse through the House.
While the Speaker could ostensibly turn to Democrats for the votes he would need to approve a spending measure, it is a move that would likely trigger an effort by the rebel faction to oust him from his plum leadership post.