WASHINGTON ― The Republican tax agenda could face an additional obstacle now that Democrat Doug Jones has defeated Republican Roy Moore in Alabama’s special Senate election on Tuesday.

Jones likely won’t be seated until January, which is after Republicans plan to send a tax bill to the president’s desk. But if for some reason the legislation were delayed, Senate Republicans would have an even thinner margin for success without Moore as a senator.

The Senate approved its version of tax reform earlier this month by a margin of 51-49, so having one fewer Republican would not necessarily imperil the bill, since Vice President Mike Pence can break a 50-50 tie.

But Sen. Susan Collins (R-Maine) has said she would only support the final version of the legislation ― a compromise version that still has to be reconciled between the different bills that passed the House and Senate ― on the condition that Congress also passes separate health legislation. And it’s not clear as of Tuesday whether Congress will do so, though Collins said she thought leaders would make it happen.

“I feel that I have a good assurance,” Collins told reporters on Tuesday.

Without Moore, Collins or Sen. Bob Corker (R-Tenn.), who voted against the Senate tax bill because it was projected to add more than $1 trillion to the national debt, Republicans would only have 49 yes votes.

President Donald Trump has used the possibility of a tax bill flop to promote Moore’s candidacy, which has been beset by numerous allegations that he made sexual advances on teenage girls when he was in his 30s.

Democrats refusal to give even one vote for massive Tax Cuts is why we need Republican Roy Moore to win in Alabama. We need his vote on stopping crime, illegal immigration, Border Wall, Military, Pro Life, V.A., Judges 2nd Amendment and more. No to Jones, a Pelosi/Schumer Puppet! — Donald J. Trump (@realDonaldTrump) December 4, 2017

Since the Senate version of the tax bill repealed the Obamacare requirement that everyone buy insurance or pay a penalty, Collins said she could only support the tax legislation if Congress passes other bills subsidizing health insurance companies.

House Speaker Paul Ryan (R-Wis.) has not indicated he supports such legislation, but he hasn’t ruled out including it in spending bills Congress needs to pass before Christmas in order to prevent the government from shutting down. Democrats, for their part, haven’t indicated they would support the bills Collins wants, either.

An Alabama state official told Reuters last month that the results wouldn’t be certified until Dec. 26 at the earliest. Republicans are hoping to be done with their tax legislation before then.

There is a recent precedent for a surprising special election delaying Senate legislation. In January 2010, after Republican Scott Brown won a special election to replace the late Sen. Ted Kennedy (D-Mass.), centrist Sen. Jim Webb (D-Va.) said he wouldn’t support any additional health care reform votes until Brown had been seated.

“In many ways the campaign in Massachusetts became a referendum not only on health care reform but also on the openness and integrity of our government process,” Webb said in a press release at the time. “I believe it would only be fair and prudent that we suspend further votes on health care legislation until Senator-elect Brown is seated.”

Ultimately, since Senate Democrats still controlled 59 seats, they had more than enough votes to approve a final health bill using the special budgetary reconciliation rules that Republicans are using today.

This article has been updated to include the example of Scott Brown’s 2010 election in Massachusetts.