WASHINGTON -- In just his second term in office, Rep. Tom MacArthur is helping to shape legislation in a way lawmakers who've been here a long time can only dream of.

But such a quick rise in Washington could come at a cost to his home state of New Jersey and perhaps his future in Congress.

MacArthur was the only New Jersey lawmaker to vote for the House Republican tax cut bill that curtailed the federal deduction for state and local taxes, and was one of only two GOP lawmakers from the state backing the health care legislation that rolled back the state's expansion of Medicaid.

In both cases, numerous independent studies showed that the bills MacArthur voted for, championed by President Donald Trump and House Republican leaders, would hurt the voters back home, leaving 540,000 additional New Jerseyans without health insurance and raising taxes on a greater percentage of state taxpayers than almost everywhere else.

"It's a high-risk game," said Ross Baker, a political science professor at Rutgers University. "It's the kind of thing you do to ingratiate yourself with the leaders and get attention at the White House. He's willing to take the risk that the stands that he takes will not alienate his constituents."

MacArthur, R-3rd Dist., said he came to Washington to get things done, not to simply to be against something.

"It's really easy to just say no," MacArthur said in a recent interview. "That to me is not helpful. To boast about inaction is a very, very poor substitute for solving problems."

He offered the amendment that paved the way for House passage of health care legislation. He successfully pushed top Republicans, including Vice President Mike Pence and House Speaker Paul Ryan, R-Wis., to keep at least a limited federal deduction for state and local taxes in the tax bill (the Senate version eliminates the entire deduction).

Trump opened up his Bedminster golf club in June to help MacArthur raise $800,000.

"Of all the backbenchers, he has the highest profile on the Republican side for sure," Baker said.

Baker said MacArthur eventually could win a leadership position in the House GOP conference. First, though, he must win re-election after backing measures opposed by most of his New Jersey colleagues and by the constituencies most affected, like the state's hospitals on health care and the business community on taxes.

"I want to hear him defend his vote," said Rep. Bill Pascrell, D-9th Dist., the only New Jersey member on the tax-writing House Ways and Means Committee and a leader of the effort to save the state and local tax deduction. "He doesn't have to explain to me. He has to explain to the voters of his district."

The House Republican health care bill would have more than doubled the number of uninsured in MacArthur's district, to 77,452 from 36,529, according to New Jersey Policy Perspective, a progressive research group. The legislation would have covered 540,000 fewer residents statewide, NJPP said.

And residents of New Jersey and three other states -- and nowhere else -- would see their taxes rise under the House GOP tax cut bill, according to a report by the Institute for Taxation and Economic Policy, another progressive research group.

In addition, both bills proved very unpopular in opinion polls. A Quinnipiac University poll released in September said three times as many U.S. voters opposed the Republicans' health care legislation as supported it, 59 percent to 19 percent. The GOP tax plan was rejected by better than 2 to 1 in another Quinnipiac poll, 52 percent to 25 percent.

MacArthur, in his statement on the House GOP tax bill, emphasized the steps he took to try to salvage the state and local tax break, including meetings with Pence, Ryan, House Majority Leader Kevin McCarthy, R-Calif., Treasury Secretary Steven Mnuchin and others.

He declared victory and endorsed the measure after Republican leaders restored a property tax deduction of up to $10,000.

"Congressman Tom MacArthur has worked tirelessly to ensure property tax deductions are included in our tax reform plan," House Ways and Means Committee Chairman Kevin Brady, R-Texas, said in a statement.

While Rep. Rodney Frelinghuysen, R-11th Dist., joined him in voting to repeal the Affordable Care Act repeal, MacArthur was the only New Jersey lawmaker to vote for a tax bill he said would provide "real relief for families and businesses."

"Their standard deduction is being doubled and their taxes are coming down," he said in a recent interview. "You have to look at all of the gives and the takes."

Nevertheless, numerous studies said the tax plan would hurt New Jersey and make it less competitive with other states. Michele Siekerka, president of the New Jersey Business & Industry Association, said the legislation would "actually make our high-tax state even less affordable."

State officials of both parties and New Jersey business organizations were among those opposing the measure. NJPP said most New Jersey taxpayers couldn't use the diminished property tax break because they no longer would have enough other expenses to exceed a standard deduction increased to $24,000 for couples.

MacArthur's support of the health care legislation caused the Cook Political Report, a Washington-based publication that tracks congressional races, to rate him as more vulnerable in 2018.

His support of the tax bill won't help his chances either, Seton Hall University political science professor Matthew Hale said.

"The more he takes positions that are out of step with his district, the more trouble he will be in," Hale said. "New Jersey in 2018 is going to be a tough place for Republicans. I think MacArthur's willingness to support Donald Trump will hurt him."

MacArthur's Democratic challenger, former White House national security adviser Andy Kim, criticized the incumbent's support of "a cruel and twisted bill that undercuts small businesses and will wreck New Jersey, all to benefit the big corporations and rich donors funding his campaign."

Peparing for a potentially tough race, MacArthur, who spent $5 million of his own money to win the seat in 2014, doubled his fundraising for 2018 to $1.2 million from $610,826 two years earlier.

Kim raised $255,187 through Sept. 30, 425 times more than the $600 raised by MacArthur's 2016 Democratic opponent, Frederick John LaVergne.

Nathan Gonzales, whose Inside Elections also rates congressional races, lists MacArthur as a safe bet for re-election because of the hurdles Kim faces.

"It's an expensive district because of the media markets, facing a wealthy incumbent who can match whatever Democrats can throw at him," Gonzales said. "It's an uphill fight."

Jonathan D. Salant may be reached at jsalant@njadvancemedia.com. Follow him on Twitter @JDSalant or on Facebook. Find NJ.com Politics on Facebook.