Sen. Joni Ernst (R-Iowa) speaks with Senate colleagues during a breakfast meeting on Capitol Hill on July 7. (Melina Mara/The Washington Post)

Oklahoma may be Trump country, but that did not prevent James Lankford (R), the state’s junior senator, from criticizing President Trump this week by saying he ought to “keep his promise” to release his tax returns.

Nor did Trump’s popularity in Iowa stop Sen. Joni Ernst (R) from telling her constituents there that she is perturbed by the president’s frequent jaunts to his Mar-a-Lago resort in Palm Beach, Fla.

“I do wish he would spend more time in Washington, D.C. That is what we have the White House for,” Ernst said at a town hall meeting Tuesday in Wall Lake, Iowa. She said she has not spoken to Trump about “the Florida issue,” but it “has been bothering not just me, but some other members of our caucus.”

As Republican lawmakers face questions from their constituents back home, some elected leaders have been willing to break with their party’s president. Although they generally support Trump’s agenda on such priorities as a tax overhaul and health care, these Republicans are criticizing the president over his continued refusal to make public his tax returns, as past presidents have, and his costly trips to Florida.

Some of those criticizing Trump are not moderates eager to establish political independence, but rather conservatives from red states who are popular with the voters who propelled Trump into office.

Sen. James Lankford (R-Okla.) answers questions during a news conference at the U.S. Capitol on Nov. 30, 2015. (Win Mcnamee/Getty Images)

The ease with which a GOP favorite such as Ernst has separated from Trump — she has criticized his Florida travel and his defiance on taxes — underscores the weak grip the president and his political operation have on the Republican Party.

“It is hard to defend in today’s world not releasing your tax returns, and it’s hard to defend playing golf at a seven-star resort when it’s a busy time and people are anxious about problems being addressed,” said Ed Rogers, a GOP operative and lobbyist.

David Carney, a GOP strategist, said finding ways to break with Trump on issues such as tax returns and travel “is a smart strategy” — especially at a moment when Trump opponents are galvanized.

“Back in 2009 and 2010, if Democrats had not been drinking Kool-Aid, saying ‘Obama makes no mistakes,’ and actually called him out on a few things, they would have had a better chance to survive the onslaught in the midterm elections,” Carney said.

White House officials say that although they wish GOP lawmakers would be fully supportive of Trump, it matters more that they back him on policies.

“The president has been pretty clear about where he is on releasing his tax returns,” White House spokeswoman Sarah Huckabee Sanders said. “People knew that before they voted in November, and he still won overwhelmingly. The American people are a lot more concerned about their own taxes than President Trump’s, and that’s what he’s focused on.”

Democratic leaders are connecting the two issues, however, threatening to block Trump’s efforts to overhaul the tax code unless he releases his tax returns so the public can determine whether he would personally benefit from the legislative changes.

Mar-a-Lago, President Trump’s private resort in Palm Beach, Fla. (Jabin Botsford/The Washington Post)

Trump has had plenty of defenders, of course. At a town hall meeting Monday in Little Rock, one man asked Sen. Tom Cotton (R-Ark.) to demand Trump release his tax returns “so we can see what kind of connections he has to different countries.”

Cotton responded by repeating the talking points employed by White House press secretary Sean Spicer.

“As far as I’m aware, the president says he’s still under audit,” Cotton said, drawing loud boos in the crowd.

Cotton continued by noting that the president filed a personal financial disclosure as a candidate and arguing that because Trump “puts his names on buildings where he has them,” his foreign connections are well known.

Cotton’s defense drew applause from some in the audience but more jeers and shouting from others. One woman stood and shook her head as the senator finished his response.

Some Republican campaign operatives said their party’s politicians would be wise to move on from the tax returns debate, recognizing that it may be nearly impossible to persuade Trump to do something he has steadfastly refused to do.

“Anyone who thought Trump would ever release his taxes is mistaken,” said Alice Stewart, a GOP consultant. “It’s not going to happen — no way, no how. Everybody has to get used to that idea.”

Still, the list of Republican senators and House members saying Trump should release his tax returns has grown to at least a dozen.

Rep. Adam Kinzinger (R-Ill.) said this week on CNN that releasing his tax returns is “the right thing to do.” Several other GOP House members — including some House Freedom Caucus conservatives — have either signed a letter calling on Trump to release his returns or backed a Democratic measure to force their release.

On Tuesday in rural Rogers County, Okla., where Trump won 76 percent of the vote last November, Lankford was asked at a town hall meeting about Trump’s decision not to release his tax returns.

“He promised he would,” Lankford responded, according to the Tulsa World newspaper. “He should keep his promise.”

Rep. Barbara Comstock (R-Va.) was quick to join her colleagues, saying in a statement Wednesday that Trump “should release his taxes voluntarily like his predecessors did before him.” She went on to say, “If the investigative committees believe that they need the president’s taxes during the course of their investigations [into Russia’s role in the 2016 campaign] then it is in their right to subpoena them.”

Trump’s frequent trips to Mar-a-Lago have also been raising concerns in the GOP. He has spent seven of the 13 weekends since he has been president at his Florida resort, often combining golf outings and leisurely meals with official business, such as the visits of Japanese Prime Minister Shinzo Abe and Chinese President Xi Jinping.

“I don’t like him going down to Mar-a-Lago, or wherever it is,” Rep. Steve Knight (R-Calif.) said during a Tuesday town hall meeting.

Comstock posited, “Camp David would be a better weekend retreat and save the taxpayers money,” referring to the official presidential retreat in Maryland that is already outfitted to secure the commander in chief and his visitors.