(Reuters) - Republican Senator Rand Paul said on Monday he will vote for a tax bill headed to the U.S. Senate floor for debate this week, settling questions about his support for the measure, although several other senators’ positions on it were still uncertain.

President Donald Trump and Republican leaders in Congress want to pass tax legislation by the end of 2017. The House of Representatives has approved its own bill. Republicans control the Senate by a 52-48 margin, leaving little room for defections.

Here is a list of Republicans whose votes could be pivotal to the bill’s fate.

RAND PAUL

Paul, a fiscal hawk with a libertarian streak who sometimes strays from the party line, said on Monday he planned to vote for the tax bill, which was headed soon to the Senate floor.

In a Fox News online opinion piece, Paul said the bill was not perfect and he would “prefer a larger cut,” but that he planned to back it because it achieved some of his goals and he could push for more changes next year.

“I plan to vote for this bill as it stands right now,” wrote Paul, of Kentucky.

RON JOHNSON

Senator Ron Johnson of Wisconsin surprised colleagues earlier this month by becoming the first Republican to announce opposition to the tax plan. That earned him a telephone call from Trump.

Johnson, formerly chief executive of a polyester and plastics manufacturer, said the legislation unfairly helps corporations over small businesses. But he has said he hopes changes could be made to win his support.

SUSAN COLLINS

Susan Collins, a moderate Maine Republican, has said she has qualms about Senate leaders’ plan to include repeal of the Obamacare individual mandate in the tax bill. The mandate requires people to buy health insurance or face a penalty.

Collins said her staff’s research showed that for some middle-class Americans, higher insurance costs stemming from repeal of the individual mandate would outweigh the benefits of the tax cuts they would receive.

She was among three Republicans who voted in July to block a Republican attempt to dismantle Obamacare, former Democratic President Barack Obama’s signature healthcare law.

BOB CORKER

Senator Bob Corker, a Trump critic who has decided not to run for re-election, has not taken a position on the tax bill.

As a deficit hawk, Corker’s main concern is red ink - the tax bill is expected to add $1.5 trillion to the national debt over 10 years.

Corker and Trump have openly feuded in recent weeks, with Corker calling the White House an “adult day care center” after Trump attacked Corker repeatedly on Twitter.

JOHN MCCAIN

Senator John McCain of Arizona, a maverick and former presidential nominee, says he will wait for the final version of the tax-cut bill before announcing his position.

The war hero infuriated Trump when he joined Collins and Senator Lisa Murkowski of Alaska in voting against the Senate bill last summer to repeal Obamacare.

McCain, who is still working after a diagnosis of brain cancer, has said he has almost no working relationship with Trump and has criticized the administration.

LISA MURKOWSKI

Murkowski of Alaska chairs the Senate Energy and Natural Resources Committee and wants to open the Arctic National Wildlife Refuge, or ANWR, to oil and gas drilling.

That provides an enticement for her to support the tax bill. Her committee has passed legislation to open the refuge to oil drilling, and the measure is expected to be attached to the tax bill. But Murkowski voted against three attempts to dismantle Obamacare in the summer, so the combination of the tax bill with a repeal of the Obamacare individual mandate may give her pause.

JEFF FLAKE

Senator Jeff Flake of Arizona, a vocal Trump critic who is not seeking re-election in 2018, has issued a statement saying he appreciated the effort to fix the tax code but was worried about the impact on the national debt.

JAMES LANKFORD

Senator James Lankford of Oklahoma, is a conservative Republican, like Flake. Lankford has been in talks with Flake and others about opposing the tax plan on the grounds that it would balloon the national deficit, Time magazine has reported.