Sen. Ron Johnson (R-Wis.) is up for reelection this cycle, but he says he’s not changing. Not one bit.

“I’ll always tell Wisconsinites the truth, to the best of my ability, and I will never vote with my reelection in mind. I’m not afraid to justify my votes. I generally have a pretty good rationale for voting the way I do,” he told The Hill in an interview from his office in the Hart Senate Office Building.

To win back the upper chamber in 2016, Democrats probably have to defeat Johnson. The freshman senator knows he is a huge target, but he isn’t shying away from his conservative credentials in a state that hasn’t voted for a Republican presidential nominee since 1984.

Johnson, 59, says he won’t let a difficult reelection race push him out of bare-knuckled confrontations with the administration or soften his resolve to reform entitlement programs.

As the new chairman of the Senate Homeland Security and Governmental Affairs Committee, he is taking a prominent role in the immigration debate by putting together a border security bill that will be the first item of the GOP’s reform agenda.

Johnson was sworn into office in 2011 after beating incumbent Democratic Sen. Russ Feingold (Wis.) in a stunning upset. This time, he will run for reelection in a presidential year, when Democratic voters typically turn out in greater numbers.

A member of the Senate Foreign Relations Committee, Johnson is positioning himself as an outspoken critic of the Democrats’ likely nominee, former Secretary of State Hillary Clinton. He has slammed her for not taking enough precautions to avert the attacks that left four Americans dead in Benghazi, Libya.

“The bigger problem for Secretary Clinton is just her dereliction of duty. She has not been held to account yet for that,” he said.

The two had a contentious exchange during Clinton’s testimony before the Foreign Relations panel in 2013, when Johnson pressed her on the administration’s initial claim that the attacks evolved from a spontaneous protest.

“Was it because of a protest, or was it because of guys out for a walk one night who decided that they’d they go kill some Americans? What difference, at this point, does it make?” Clinton asked.

Johnson’s Homeland Security Committee gavel gives him a platform to speak out on another fast-rising issue: the threat posed by militant Islamic groups around the world.

“We’re not the ones devising the strategy. Only the commander in chief can do that. So, [President Obama] has to establish the goal. He has to define what that looks like. What do you mean by defeat? Is it just in Iraq? Is it in Iraq and Syria?” he asked.   

Democrats say Johnson’s refusal to distance himself from his party will come back to haunt him next year.

“Without a doubt, Ron Johnson is the most vulnerable senator in the country,” said Justin Barasky, communications director of the Democratic Senatorial Campaign Committee. “He has distinguished himself in a variety of ways, be it his record, his public posturing, his partisan warrior stance he’s used to taking on every issue.”

Barry C. Burden, a professor of political science at the University of Wisconsin-Madison, said, “He’s really latched onto two or three Washington issues to focus on. … When he arrived, it was about the healthcare law and wanting to repeal that, and then moving on to Benghazi and other foreign policy issues. To his credit, he hasn’t relented on any of those things. They’re still his focus, even though we’re a year and a half from the election.”

There’s speculation that Feingold might want a rematch and some chatter that veteran Rep. Ron Kind (D-Wis.) might jump in the race.

Republicans say that, while Johnson has stuck to his conservative principles, it won’t hurt his reelection bid, because he eschews the heated rhetoric of some of his colleagues.

“He’s conservative, but he’s not somebody who’s alarming. He has a reassuring presence. Some conservatives don’t have it. He’s conservative and responsible in his rhetoric,” said Peter Wehner, former director of the White House Office of Strategic Initiatives under George W. Bush.

Johnson, he said, feels free to speak his mind on thorny political and policy topics because he’s not a career politician. The Wisconsin Republican spent most of his professional life in the business world running a plastics manufacturing company. He never visited Washington before running for the Senate.

Privately and publicly, Johnson has pressed Obama on the debt, noting that the Congressional Budget Office has projected federal spending will exceed federal revenue by about $126 trillion over the next 30 years.

“Know what he said to me? He said, ‘Ron, we can’t show the American public numbers that big. If we do, they’ll get all scared, throw up their hands, give up all hope,’ ” Johnson recalled of his conversation with Obama. “He said, ‘Besides Ron, we can’t do all the work; we have to leave some work for future presidents, future Congresses.’

“It would be funny if it weren’t so sad,” Johnson added.

Johnson will be a central player in this year’s fiscal debate as a member of the Budget Committee. While he views the growth of Social Security and Medicare spending as a dire problem, he has enough of a sense of political self preservation to advise his GOP colleagues not to propose cuts to those programs unilaterally.

“I’d say that’s probably not the smartest thing to do politically,” he said.

Instead, Johnson wants them to lay out a  “solution menu” of options to extend the solvency of those programs.