House Republicans barely managed to pass their Obamacare repeal bill earlier this month, and they now face the possibility of having to vote again on their controversial health measure.

House Speaker Paul Ryan hasn’t yet sent the bill to the Senate because there’s a chance that parts of it may need to be redone, depending on how the Congressional Budget Office estimates its effects. House leaders want to make sure the bill conforms with Senate rules for reconciliation, a mechanism that allows Senate Republicans to pass the bill with a simple majority.

Republicans had rushed to vote on the health bill so the Senate could get a quick start on it, even before the CBO had finished analyzing a series of last-minute changes. The CBO is expected to release an updated estimate this week.

"Unaware," said Representative Jeff Denham of California, with noticeable surprise Thursday, when advised that his party leaders still hadn’t sent the bill over to the Senate.

One senior GOP aide downplayed any concern over the potential trouble from the CBO report, depicting it as hypothetical, and saying that leaders will cross that bridge if they need to.

According to several aides and other procedural experts, if Republicans send the bill to the Senate now and the CBO later concludes it doesn’t save at least $2 billion, it would doom the bill and Republicans would have to start their repeal effort all over with a new budget resolution. Congressional rules would likely prevent Republicans from fixing the bill after it’s in the Senate, the aides said.

In the Senate, the bill must hit separate $1 billion deficit reduction targets in the jurisdiction of the Finance Committee and the chamber’s health committee. Republican aides said failing to meet those numbers would force the House to fix the bill even if the legislation meets the overall cost-savings target.

If Republican leaders hold onto the bill until the CBO report is released, then Ryan and his team could still redo it if necessary. That would require at least one more House vote of some sort.

Ryan told conservative radio host Hugh Hewitt on Friday that he doesn’t think the House will need to vote again on the health law. “We just want to, out of an abundance of caution, wait to send the bill over to the Senate when we get the final score,” Ryan said.

That vote could be cloaked in some kind of arcane procedural move, but it would still be depicted as a proxy for yet another vote on the same bill. Reluctant Republicans will once again be forced to decide whether to back it, only this time, they would also be saddled with the CBO’s latest findings about the bill’s costs and impacts.

Republicans had a sizable deficit reduction cushion—$ 150 billion—before several amendments were added to the bill at the last minute, including changes allowing states to legalize much skimpier health insurance plans.

It’s unclear what assumptions the CBO will make about what states will do with that newly created flexibility. If millions of people sign up for much cheaper, minimal insurance, that could trigger billions—and potentially even hundreds of billions—in costs over a decade because of the House bill’s health insurance tax credits.

GOP leaders never said publicly they were planning to hold on to the bill for two weeks or longer. The speaker and other Republicans urgently pushed their May 4 floor vote, despite a polarized Republican conference, using the frantic final hours to win over holdouts. Even so, 20 Republicans still voted against the bill.

That 217-213 tally appeared to be a rare legislative victory for them and President Donald Trump, even if the vote was a difficult one for some rank-and-file House Republicans, who had qualms. Some have since been hit with protests in their districts and anger from constituents. Now, two weeks later, the American Health Care Act, H.R. 1628, hasn’t been transmitted from the House to the Senate, according to Senate Bill Clerk Sara Schwartzman.