Sen. Dean Heller wanted to make clear to his Nevada constituents that his fingerprints were all over the GOP’s tax overhaul that passed the Senate early Saturday morning.

“I was asked earlier today if I read the tax bill…Read it? I helped write it!” he tweeted hours after the measure passed -- a message now pinned to the top of his campaign Twitter page.

With that statement, Heller doubled down on what he had already made clear in the weeks leading up to the vote in the upper chamber: He’s all in on the GOP tax reform. As the most vulnerable Senate Republican up for re-election next year, and the only one running in a state that Hillary Clinton won, Heller is facing stiff headwinds in what is likely to be a challenging national environment.

With a target on his back from Democrats and a Republican primary challenger, Heller has embraced tax reform as a critical issue, and has been aggressive in touting his support for it. But Democrats are also convinced that his all-in support is a gift to their efforts to unseat him. Ben Ray, a spokesman for the Democratic Senatorial Campaign Committee, joked that Heller’s tweet should be an “in-kind contribution” to the party.

The situation in Nevada is a microcosm of the nationwide debate about tax reform: Republicans are convinced, despite negative polling numbers, that their bill will grow in popularity after it gets enacted and that it is a political necessity for their 2018 election chances. Democrats, meanwhile, are similarly convinced that Republicans have erred, and that the unpopular legislation will be easy to campaign against next year.

The legislation isn’t final yet, but passage in the Senate was a critical step, particularly after Obamacare repeal measures failed there earlier this year. The two chambers are expected to negotiate the differences in their bills in the coming weeks, and hope to put a final version on President Trump’s desk before the end of the year.

As a member of the Senate Finance Committee, Heller played a central role in shaping the legislation. He helped craft the doubling of the child tax credit to $2,000, one of the key provisions to help boost the defense of the bill as a tax cut for middle-class families. Last month, Heller released his first television ad of the election cycle, highlighting his call to keep the Senate running longer hours to confirm judges and “pass real tax reform, with real tax cuts for families and small businesses.”

In an op-ed in the Reno Gazette Journal late last month, Heller touted that tax credit, as well as other provisions he argued would be winners for his constituents. He argued it would “boost middle-class income by nearly $2,500 and add more than 8,300 jobs in Nevada.”

“As tired as I am right now, I think I am running on adrenaline … after we were able to achieve such a historic piece of legislation,” Heller said over the weekend, according to The Nevada Independent.

Still, Democrats are mobilizing against it. Rep. Jacky Rosen, the Democrat challenging Heller next year, released digital ads attacking him for a “broken promise” on the national debt, citing independent analyses that show the tax legislation could add as much as $1 trillion to the deficit over a decade. The DSCC is also running digital ads in the state (and in several others) spotlighting the fact that the GOP bill would raise taxes on some middle-income Americans.

“Instead of delivering on his promise of tax relief for the middle class, Senator Heller betrayed his constituents again by voting to increase taxes and health care costs for working families, increase the national debt by $1 trillion, and give billionaires a massive tax cut,” Rosen said in a statement after the Senate vote.

Still, before Heller can face off against a Democrat, he’ll have to win a primary against Danny Tarkanian, a Republican who has lost five previous runs for office but is challenging the incumbent by arguing he is insufficiently supportive of Trump.

In an interview with RealClearPolitics, Tarkanian said he didn't think Heller would see any benefit with Republican primary voters for his efforts on tax reform.

"We have a Republican-controlled Congress and presidency. Tax reform should be a given, as should the repeal of Obamacare and other issues that the Republicans campaigned on," he said. "This isn’t something that should surprise anybody. If this is Dean Heller’s chief argument for re-election, it’s a really disappointing argument.

“Maybe President Trump is thankful that he finally voted with him on one of his policy issues," Tarkanian added. "That’s been a change for him."

Tarkanian said he would have supported the legislation the Senate passed last week, though he didn't support several aspects of it. He said he backed lowering the corporate tax rate, doubling the standard deduction and increasing the child tax credit, but criticized Republicans’ decision to phase out most of the tax cuts for individuals in 2025 -- independent analyses have shown that many middle-income Americans could see significant tax increases because of that decision. Republicans phased out those cuts to allow the bill to pass under reconciliation rules to avoid a filibuster, and argue that when the time comes, lawmakers will vote to extend them rather than allowing people to see tax hikes.

"They’re kicking the can down the road and hoping the legislators in office at that time will be pressured enough to maintain those tax breaks," Tarkanian said. "I don’t believe that’s fair. They ought to handle it now.”

Heller appeared vulnerable earlier this year, especially after announcing his opposition to initial versions of the Obamacare repeal bill in the Senate. Trump criticized him, and the president’s allies planned to run ads against Heller in Nevada. He eventually came around to supporting the GOP legislation, and then sponsored the final iteration this fall.

On taxes, he’s taken a much more straightforward path by working closely with the administration and Republican leadership to pass the bill. Marc Short, the White House director of legislative affairs, told RealClearPolitics Heller was helpful in winning over support from some Republicans who were hesitant to support the legislation.

“I think that he views passing tax reform as critical to the 2018 midterm elections not just for him, but for all of us,” Short said. “When you have a member who’s considered the most vulnerable saying, ‘Hey, guys -- I’m obviously up in a very difficult election cycle and I think we need to be all in on this,’ I think that helps other members get there.”