WASHINGTON (AP) — Most Republican leaders were silent or supportive of President Donald Trump’s public call for another foreign government, China, to investigate his political foe, while a few voiced concern that the president was trying to enlist a rival power in his reelection effort.

Several House and Senate leaders stayed mum Friday as Trump escalated the controversy that has fueled an impeachment inquiry and plowed through another norm of American politics. Foreign interference in elections has long been viewed as a threat to U.S. sovereignty and the integrity of democracy, and soliciting foreign help in an election is illegal.

But Trump found support in his willingness to openly challenge that convention. Vice President Mike Pence made clear he backed the president and believes he is raising “appropriate” issues. Other allies agreed.

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“I don’t think there’s anything improper about doing that,” GOP Sen. Ron Johnson, chairman of the Homeland Security Committee, said of Trump’s call on China to investigate the business dealings of Hunter Biden, the son of leading Democratic presidential candidate Joe Biden.

On Friday morning, Utah Sen. Mitt Romney dissented: “By all appearances, the President’s brazen and unprecedented appeal to China and to Ukraine to investigate Joe Biden is wrong and appalling.”

He added, in a tweet: “When the only American citizen President Trump singles out for China’s investigation is his political opponent in the midst of the Democratic nomination process, it strains credulity to suggest that it is anything other than politically motivated.”

Romney and Nebraska Sen. Ben Sasse appeared to be the only Republicans going public with concerns. Sasse said in a statement to the Omaha World-Herald: “Americans don’t look to Chinese commies for the truth. If the Biden kid broke laws by selling his name to Beijing, that’s a matter for American courts, not communist tyrants running torture camps.”

Those concerns did not address new evidence that emerged late Thursday and appeared to corroborate some of the allegations contained in a whistleblower report that helped trigger an impeachment investigation of Trump.

House Democrats released a trove of text messages showing U.S. diplomats conducted a campaign to push Ukraine into launching investigations of the Bidens and the 2016 election. Neither Senate Majority Leader Mitch McConnell nor House Minority Leader Kevin McCarthy responded to a request for comment.

The responses followed a familiar pattern in the age of Trump. As the president broke another political barrier, his party leaders made no public effort to rein him in. Critics have argued that reaction has only emboldened the president, while doing lasting damage to the party and the presidency. Trump allies argue the president’s rule-breaking rhetoric is not as important as his policies, which they support.

But the silence this time also reflects a sharper dilemma for Republicans. As Democrats pursue an impeachment investigation , Republicans have been struggling with how best to shield themselves — and the unpredictable president who may decide their political fortunes — from the steady drip of new revelations. With little guidance from the White House, lawmakers have tried to say as little as possible, blame Democrats or express vague optimism about the investigative process. Trump’s remarks Thursday demonstrated the limits of that strategy.

Standing outside the White House, Trump defended himself against allegations that he privately pressured Ukraine to investigate the Bidens by inviting a geopolitical rival to launch a probe.

“China should start an investigation into the Bidens,” Trump said after being asked about trade negotiations with the country.

Trump on Friday argued that he not specifically targeting a political foe, but merely pushing countries to clean up corruption. Although there is no evidence that the Bidens were involved in criminal corruption in either Ukraine or China, Republicans quickly took up the explanation.

Pence argued that the Bidens’ ties to Ukraine are of interest to the American people.

“There are legitimate questions that ought to be asked. We will continue to ask them because the American people have a right to know whether or not the vice president of the United States or his family profited from his position,” he said.

One of the party’s most vulnerable senators, Arizona’s Martha McSally, stood at Pence’s side at the stop in Scottsdale. McSally has blasted Democrats for launching an impeachment investigation focused on Trump’s pressure on Ukraine, but has not commented on the whistleblower report and the loose transcript of the phone call that prompted the probe. Her office had no comment about whether she thought Trump’s statement Thursday was appropriate.

In North Carolina, Sen. Thom Tillis, whom Democrats hope to topple in 2020, also stood by the president.

“We’ll see what comes out of their impeachment inquiry. They’re not drawing up articles of impeachment yet,” Tillis told The Associated Press in an interview Monday. “What I’ve said is if they’re basing this entire process on a now public, unredacted transcript and the whistleblower complaint, certainly that doesn’t rise to a level of impeachment, in my opinion.”

Asked about his reaction to the public statements Thursday, Tillis’ office responded with a statement: “Democrats and the mainstream media are using anything and everything to justify impeaching the president and removing him from office.” His office referred back to that statement Friday morning after the texts were released.

At a town hall meeting in western Iowa, Sen. Joni Ernst was asked about Trump’s Ukraine call and request for foreign intervention. “We’re going to move onto another question, but what I would say is we can’t determine that yet,” Ernst said. She said the Senate Intelligence Committee would evaluate it.

She was blunt about the limits of her influence on the president.

“I can yay, nay whatever. The president is going to say what the president is going to do.” Ernst said, saying it was up to member of Congress to make sure “we remain strong in the face of adversary.”

The office of Sen. Cory Gardner of Colorado, widely considered the most vulnerable Republican senator, issued a statement that didn’t reference Trump’s request of China. “The Senate Intelligence Committee is a serious and respected body that is looking into this in a bipartisan fashion,” the statement said.

The offices of several other senators up for reelection next year alongside the president, including Sen. Susan Collins of Maine, also did not respond.

House Democrats are investigating Trump’s July 25 call to Ukraine President Volodymyr Zelenskiy, in which Trump pressed the newly elected leader to look into the Biden family.

Hunter Biden served on the board of a Ukrainian gas company at the same time his father was leading the Obama administration’s diplomatic dealings with Kyiv. Though the timing raised concerns among anti-corruption advocates, there has been no evidence of wrongdoing by either the former vice president or his son.

Riccardi reported from Denver. Associated Press writers Scott Bauer in Madison, Wis.; Sara Burnett in Chicago; Jonathan J. Cooper in Phoenix; Scott McFetridge in Des Moines, Iowa; Lindsay Whitehurst in Salt Lake City; and Gary D. Robertson in Raleigh, N.C., contributed to this report.