Senate Republicans are hoping for tax reform by Christmas, but they still need to make sure to get a few more members of their party on board first.

In order to do that, GOP lawmakers are considering different measures to garner more support, including implementing an automatic trigger that would raise taxes if the legislation failed to garner as much revenue as expected.

Republicans only have two votes to spare in the Senate, where they hold a 52 to 48 edge. Vice President Mike Pence would break the tie, if needed.

Here’s a look at which Republicans still have concerns about the current tax reform measure.

Steve Daines

U.S. Senator Steve Daines (R-MT) smiles after he was ceremonially sworn-in by Vice President Joseph Biden in the Old Senate Chamber on Capitol Hill in Washington January 6, 2015.     REUTERS/Larry Downing   (UNITED STATES - Tags: POLITICS HEADSHOT) - GM1EB170DHP01

Sen. Steve Daines, R-Mont., said he is optimistic that changes could be made to the tax reform bill that would get him on board with the plan.

 (Reuters/Larry Downing)

Sen. Steve Daines, R-Mont., is a no so far on the tax reform legislation but told Fox News Tuesday that he’s had “very construction and positive conversations” with President Trump and others in the administration who have a hand in overhauling the nation’s tax process.

Daines said he is “optimistic” that the improvements could be made to the bill before it’s time to vote – in which case, he could change his mind.

Ron Johnson

Chairman of the Senate Homeland Security and Governmental Affairs Committee Ron Johnson (D-WI) questions Kirstjen Nielsen (unseen) on her nomination to be secretary of the Department of Homeland Security (DHS) in Washington, U.S., November 8, 2017.   REUTERS/Joshua Roberts - RC12EE404750

Sen. Ron Johnson, R-Wis., has warned that he could vote against the GOP tax reform measure.

 (Reuters/Joshua Roberts)

Wisconsin’s Sen. Ron Johnson originally wasn’t too big of a supporter of the tax bill, but after meeting with Senate leadership and Trump, he voted it through the Finance Committee. 

He told Fox News that Trump promised to fix some of the problems he had with the measure and would work with them as the bill moves to the full Senate. Johnson voted to move the legislation out of the Senate Budget Committee Tuesday and said he’s been assured that his concerns with pass-throughs will be addressed. 

Susan Collins

U.S. Senator Susan Collins speaks at the Penobscot Bay Regional Chamber of Commerce's Quarterly Business Breakfast in Rockport, Maine, U.S., October 13, 2017. REUTERS/Joel Page - RC1A014FF7B0

Sen. Susan Collins, R-Maine, said she was optimistic about tax reform after meeting with President Trump.

 (Reuters/Joel Page)

When it came to Republicans’ efforts to overhaul the healthcare system, Sen. Susan Collins, R-Maine, was not on board. Now Republicans are looking to see if she’ll join them on taxes.

While her position is still unknown, she has reportedly said there are things she is “trying to change” regarding the current legislation. After meeting with the president Tuesday, Collins said she was feeling “optimistic” about tax reform, the New York Times reported.

Bob Corker

U.S. Senator Bob Corker (R-TN) attends the Senate Budget Committee markup of the FY2018 Budget reconciliation legislation on Capitol Hill in Washington, U.S., November 28, 2017.   REUTERS/Joshua Roberts - HP1EDBS1M2W29

Sen. Bob Corker, R-Tenn., is focused on how any tax reform legislation would impact the federal deficit.

 (Reuters/Joshua Roberts)

Sen. Bob Corker, R-Tenn., is one Republican who still hasn’t made up his mind – at least publicly – about his vote on tax reform. He has said he’s concerned about how the legislation will impact the national debt, but he did vote it through the Senate Budget Committee Tuesday.

Corker wants to include a “backstop” or trigger in the legislation that would increase revenues even if the plan falls short. 

After Trump’s meeting with Senate Republicans, Corker said, “I think we’re getting to a very good place on the deficit issue.”

“While we are still working to finalize the details, I am encouraged by our discussions.”

Jeff Flake

U.S. Senator Jeff Flake (R-AZ) walks past journalists after announcing he will not run for reelection on Capitol Hill in Washington, DC, U.S. October 24, 2017. REUTERS/Joshua Roberts - RC115CA83EE0

Sen. Jeff Flake, R-Ariz., has stood at odds with President Trump, especially since he announced his retirement from Congress.

 (Reuters/Joshua Roberts)

Like Sen. Bob Corker, Jeff Flake has been publicly at odds with the Trump administration – especially since he announced his impending retirement from the Senate.

And also like Corker, Flake, R-Ariz., has not publicly announced where he stands on the tax reform legislation but has expressed concern about its impact to the country’s debt.

James Lankford

Senator James Lankford (R-OK) speaks during Senate Intelligence Committee hearing to answer questions related to Russian use of social media to influence U.S. elections, on Capitol Hill in Washington, U.S., November 1, 2017.   REUTERS/Joshua Roberts - RC176A395460

Sen. James Lankford, R-Okla., said he is for tax reform but wants to make sure it’s done “right.”

 (Reuters/Joshua Roberts)

Sen. James Lankford, R-Okla., wants to make sure the legislation doesn’t increase the federal deficit and has yet to publicly announce his plan for the bill.

“What changes might be needed in the tax code in the days ahead, to be able to adjust in what scenario,” Lankford said. He’s maintained that he’s not against tax reform but wants to make sure it’s done “right.”

John McCain

Sen. John McCain (R-AZ) looks on at a press conference about the National Defense Authorization Act in Washington, U.S., October 25, 2017. REUTERS/Aaron P. Bernstein - RC12A8A96500

Sen. John McCain, R-Ariz., praised the Senate Finance Committee for passing the tax measure through the use of regular order.

 (Reuters/Aaron P. Bernstein)

While Sen. John McCain, R-Ariz., hasn’t announced how he plans to vote, he did praise the Senate Finance Committee for passing the tax plan through the use of regular order earlier this month.

Like others, McCain is also considered a deficit hawk when it comes to the tax bill and its impact on the federal deficit.  

Jerry Moran

U.S. Senator Jerry Moran (R-KS) delivers remarks at the public launch of the U.S. Agriculture Coalition for Cuba while at the National Press Club in Washington, January 8, 2015.  REUTERS/Larry Downing  (UNITED STATES - Tags: POLITICS BUSINESS AGRICULTURE) - GM1EB190EF201

Sen. Jerry Moran, R-Kan., did not commit to the tax reform measure at a town hall event.

 (Reuters/Larry Downing)

At a town hall event last week, Sen. Jerry Moran, R-Kan., refused to commit to the current tax legislation but did say that he is “for some tax bill.”

“Can we find taxes to cut that grow the economy? We don’t want to increase the debt and deficit as a result of tax cuts,” Moran said, according to the Topeka Capital-Journal. “My goal is to find out which taxes you cut can actually help create more jobs, better jobs, higher-paying jobs … and which ones don’t do that. Not all of them do that.”

Lisa Murkowski

Senator Lisa Murkowski (R-AK) arrives for a Senate health care vote on Capitol Hill in Washington, U.S., July 27, 2017. REUTERS/Yuri Gripas - RC1350CE4CA0

Sen. Lisa Murkowski, R-Alaska, could potentially be convinced to vote on the tax reform measure if it includes certain provisions for her state.

 (Reuters/Yuri Gripas)

A more moderate Republican, Sen. Lisa Murkowski of Alaska has not yet committed to backing the tax reform measure.

But Murkowski could potentially be swayed into voting for the bill if it comes with a provision that would allow drilling in Alaska’s Arctic National Wildlife Refuge – something that she’s long pushed for.

Marco Rubio

Senator Marco Rubio (R-FL) speaks in support of  Kirstjen Nielsen's nomination to be secretary of the Department of Homeland Security (DHS) in Washington, U.S., November 8, 2017.   REUTERS/Joshua Roberts - RC140B6B1720

Sen. Marco Rubio, R-Fla., has been an advocate for an increase in the child tax credit.

 (Reuters/Joshua Roberts)

Sen. Marco Rubio, R-Fla., told WFOR-TV that when it comes to tax reform, he’s looking for two components: a proposal that will make the U.S. “more competitive” and “take care of workers.”

Rubio has pushed for an expansion of the child tax credit and wants to make “it fully refundable against payroll taxes.”

Fox News’ Peter Doocy and The Associated Press contributed to this report.

Kaitlyn Schallhorn is a Reporter for Fox News. Follow her on Twitter @K_Schallhorn.