WASHINGTON >> One of the loudest critics of GOP health legislation is not a Democrat or even a conservative rebel, but a Republican loyalist and staunch defender of President Donald Trump.

Freshman Sen. Tom Cotton of Arkansas is not known for clashing with leadership or plotting with conservative trouble-makers in the House, as Sens. Rand Paul of Kentucky and Ted Cruz of Texas are wont to do. Instead the 39-year-old Iraq and Afghanistan combat veteran, the nation’s youngest senator, has carved out a hawkish and bold profile on foreign policy that many see as a platform for a future presidential run.

And now Cotton, who won his seat in 2014 partly by lambasting his Democratic predecessor for supporting Barack Obama’s health care bill, is very publicly on the attack against the House health legislation backed by Speaker Paul Ryan and the White House.

Cotton is warning House Republicans against voting for the bill, cautioning that it could die in the Senate and cause political pain for all its supporters, and threatening to withhold his own vote unless it becomes more to his liking.

“There’s a long history in modern politics of House members walking the plank for legislation that not only fails to become law but never even gets a vote in the Senate,” Cotton, a one-term House member before coming to the Senate, said in an interview in his office Thursday. “I don’t want to see something like that happen to my old friends in the House of Representatives.”

He warned, “The House majority could be at risk if we get health care reform wrong.”

The House GOP bill is the party’s attempt, with control of both chambers of Congress and the White House, to finally make good on seven years’ worth of promises to repeal and replace Obama’s health care law. It eliminates the “Obamacare” mandate to buy health insurance, limits tax credits and unwinds a Medicaid expansion, but some conservatives say it doesn’t go far enough. Cotton criticizes the legislation for failing to adequately keep down health care costs and premiums, arguing that the bill must do more to eliminate regulations from the Affordable Care Act.

Cotton’s opposition, which he’s broadcast in multiple TV and radio interviews and over Twitter, has raised eyebrows in the Capitol where a number of GOP senators have misgivings about the bill, but many are more restrained in expressing them. Ryan and other GOP leaders have chafed at Cotton’s repeated calls to slow down the health care bill, which leadership is eager to get through Congress quickly.

“We’ve been working at this literally for seven years,” said the No. 2 Senate Republican, John Cornyn. “This isn’t going to get any easier the longer we leave it hanging out there.”

Asked on Hugh Hewitt’s radio show about Cotton’s opposition, Ryan replied, “I love this, because we’ve gotten criticized by other folks in the conservative movement for waiting too long.”

Cotton’s making trouble for Ryan on another issue, too, taking an outspoken stance against a proposed “border-adjustment tax.” House leaders want to levy the tax on imports to pay for lowering corporate rates in a planned tax overhaul. The border-adjustment tax is opposed by large retailers including WalMart, which is headquartered in Arkansas, and Cotton slammed it on the Senate floor and published an opinion piece in USA Today this week denouncing it as “a theory wrapped in a speculation inside a guess.”

Cotton’s stance on the health legislation also reflects realities on the ground in his state, where health advocates credit the Affordable Care Act with cutting how much hospitals are spending on care for uninsured patients and for a dramatic drop in the state’s uninsured rate. The percentage of Arkansans uninsured dropped from 22.5 percent in 2013 to 10.2 percent in 2016, according to the Gallup-Healthways survey.

Cotton disputes the suggestion that Obamacare is working well in Arkansas or enjoys much popularity, but acknowledges high anxiety among his constituents about what happens next. And though he’s been one of Trump’s unwavering supporters, including using his position on the Armed Services Committee to defend the president over Russia, he’s not ready to fall in line yet, especially given the mixed signals Trump has sent on whether he actually supports the bill as-is.

“President Trump has repeatedly said that this bill is not his bill, it is a preliminary first step and open for negotiations,” Cotton said. “That’s what we should have done from the very beginning.”