The addition of the East Wing money turns what would have likely proven an easy party-line vote into a potentially much heavier lift. Ultimately, 50 of 53 Republican senators will have to support the White House funding; if not, the whole bill is at risk.

The $1 billion language is fairly loose in its current form, and the Trump administration just stretched funds to pay employees during a shutdown, so senators could also specify that money cannot go directly to the ballroom. That prospect is likely to cause more intraparty debate.

A majority of senators could also decide to strip out the provision altogether; Democrats are almost certain to force votes on the money. Sen. Lisa Murkowski, R-Alaska, voted against the budget, giving GOP leaders little room for error with the final product.

Sen. Rand Paul, R-Ky., who voted against the budget resolution setting up the party-line bill, argues that the GOP Senate could put a small amount of money toward the project to address ongoing litigation over whether Congress needs to approve it, but doesn’t support Congress paying for it in full.

Many conservatives expressed concern over taxpayer money going to the ballroom, however, and have sought to authorize the project without funding it directly. It’s not clear yet whether that opposition would soften if the money were restricted to security.

Sen. Ron Johnson, R-Wis., told Semafor that it “seems to be a reasonable long-term investment for security reasons, and providing a larger venue that is often needed.”

“I’d rather spend federal tax dollars on capital assets versus government programs that are rife with waste and fraud,” Johnson added.