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 handful 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. The quiet continued as House Democrats released a trove of text messages showing U.S. diplomats conducted a campaign to push Ukraine to investigate former vice president Joe Biden, a leading candidate for the Democratic nomination to face Trump next November, and Biden’s son, Hunter.

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.

“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 Bidens.

Dissent came from familiar corners. Utah Sen. Mitt Romney tweeted: “By all appearances, the President’s brazen and unprecedented appeal to China and to Ukraine to investigate Joe Biden is wrong and appalling.”

Nebraska Sen. Ben 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.”

In contrast, neither Senate Majority Leader Mitch McConnell nor House Minority Leader Kevin McCarthy responded to requests for comment Friday.

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.

Some Republicans appeared eager for the controversy to simply not exist. “I don’t think it’s a real request,” Florida Sen, Marco Rubio, a prominent China critic, told reporters on Friday. “I think he did it to get you guys. I think he did it to provoke you to ask me and others and get outraged by it.”

The president and his defenders indicated he was quite serious on Thursday. 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.

Romney tweeted the counter argument: “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.”

House Democrats are investingatin whether Trump abused his power when he pressure Ukraine President Volodymyr Zelenskiy to look into theories about Ukraine meddling in the 2016 and a separate allegation about Hunter Biden’s business ties.

The younger 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.

The question of whether to dodge or defend is perhaps most critical for the Republican senators in competitive races next year. Those Republicans have little incentive to criticize the president because can’t risk alienating Trump’s base voters. But their futures also depend on peeling off enough swing voters who turned against Trump last year. An impeachment vote will force them to pick sides — an lose some support — on either side.

Most of those senators have tread carefully — and quietly — on the subject.

Arizona’s Martha McSally, stood at Pence’s side at the Thursday stop in Scottsdale, but did not commented on the matter. She has criticized Democrats for launching an impeachment investigation, but 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.

The office of Sen. Cory Gardner of Colorado, widely considered the most vulnerable Republican senator and a special guest at a Trump re-election fundraiser this weekend, issued a statement Thursday 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.

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

Asked about his reaction to the public statements Thursday, Tillis’ office responded with: “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.

Sen. Susan Collins of Maine, another Republican in a tough reelection race, did not respond to a request for comment.

While avoiding weighing on the propriety of the Trump’s remarks, one GOP senator was blunt about the limits of the party’s 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.”

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Riccardi reported from Denver. Associated Press writers Alan Fram in Washington, 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.