The escalating controversy over President Trump’s phone conversation with Ukraine’s president has ignited a battle on Capitol Hill over Democrats’ demands for a copy of the whistleblower complaint against Trump, as some liberal lawmakers threatened subpoenas while Republicans called for restraint while they gather facts.

Democrats have seized on allegations that Trump pressured Ukrainian President Volodymyr Zelensky to investigate dealings involving 2020 presidential candidate Joe Biden’s son, Hunter, citing those claims to revive calls for impeachment.

Trump has denied any wrongdoing, but Democrats have been moving full steam ahead, calling for the whistleblower complaint to be released to lawmakers.

SOURCE SAYS WHISTLEBLOWER DIDN'T HAVE ‘FIRSTHAND KNOWLEDGE’ OF TRUMP CALL WITH UKRAINE PRESIDENT

“The Senate Republican ‘see no evil, hear no evil’ attitude is unacceptable and must change,” Senate Minority Leader Chuck Schumer said on Senate floor Monday. “This again is an issue of solemn obligation. There is no wiggle room here, none.”

The New York Democrat earlier in the day wrote a letter to Senate Majority Leader Mitch McConnell asking him to issue a subpoena and hold hearings over the complaint.

In a floor speech Monday afternoon, the Kentucky Republican rebuffed those calls from Democrats, saying the Senate Intelligence Committee has been following an established process and was working to hear from the intelligence community's inspector general this week.

“It is regrettable that House Intelligence Committee Chairman [Adam] Schiff and Sen. Schumer have chosen to politicize the issue,” McConnell said, calling for looking into the matter in an “appropriate, deliberate bipartisan manner.”

In a statement Monday, Iowa GOP Sen. Chuck Grassley called for lawmakers not to rush to judgment.

“One thing we do know is that rampant speculation by politicians and the media is not helpful,” he said. “That’s how the false Russia collusion narrative took root.”

He added: “Let’s not repeat the mistakes of the past. Going forward, it’s important to respect the law and the whistleblower’s confidentiality while we gather the facts of the case. And of course, transparency is always the best policy so long as we don’t endanger national security.”

On Wednesday, Democrats chairing three House committees sent a letter to Secretary of State Mike Pompeo asking the department to produce documents related to the complaint, or face subpoenas.

“Seeking to enlist a foreign actor to interfere with an American election undermines our sovereignty, democracy, and the Constitution, which the President is sworn to preserve, protect, and defend,” the chairmen wrote. “Yet the President and his personal attorney now appear to be openly engaging in precisely this type of abuse of power involving the Ukrainian government ahead of the 2020 election.”

The letter was sent by Schiff, House Foreign Affairs Committee Chairman Eliot Engel of New York and Oversight Committee Chairman Elijah Cummings of Maryland.

At least one Republican lawmaker, however, has called for the release of the transcript.

“At this stage, given the seriousness of the allegations, it’s very important that the transcript and potentially as well the whistleblower come forward," said Utah Republican Sen. Mitt Romney, an occasional Trump critic.

Meanwhile, a source told Fox News on Monday that the whistleblower who sparked the complaint did not have “firsthand knowledge” of the conversation. The source said that it was made clear in the complaint itself that the whistleblower did not have direct knowledge of the July phone call between Trump and Zelensky.

Fox News has learned that typically, multiple U.S. officials would be on such calls with the president, but this would indicate the whistleblower was not one of those people. It's unclear if the individual read a transcript of the call, heard about it in conversation or learned of it another way.

These new details have fed into skepticism about the allegations from Trump’s allies in Congress, with some likening it to how Democrats rushed to call for Supreme Court Justice Brett Kavanaugh’s impeachment last week. Some Democrats backed off after The New York Times amended an explosive article on new college-era allegations of sexual misconduct against Kavanaugh to make clear that the alleged victim did not have any recollection of the alleged episode.

On Fox News’ “Outnumbered Overtime,” GOP Rep. Chris Stewart of Utah on Monday likened the two situations and called for restraint regarding the whistleblower complaint. “I think it’s fair to just take a breath, and say let's just find out the facts and see what happens,” he said.

Republicans also have been trying to return the focus to Biden. Trump allies have claimed son Hunter improperly benefited from business dealings in Ukraine with energy company Burisma Holdings as a member of its board and questioned whether his father, the onetime vice president, helped protect him by seeking the ouster of prosecutor Viktor Shokin, who was looking into the company's owner.

Trump, in a Sunday night tweet, said the Ukrainian government backed him up by saying he did not pressure them during the phone call. In the same tweet, he said the “real story” was Biden pressuring Ukraine into firing Shokin.

Burisma hired Hunter Biden in April 2014, two months after Ukraine's Russia-friendly president was ousted amid protests and as his father was involved heavily in U.S. efforts to support the new pro-Western government and its pledge to fight corruption. The hiring of the younger Biden immediately raised concerns that the Ukrainian firm, whose owner was a political ally of the ousted president, was seeking to gain influence with the Obama administration.

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Two years later, Biden, as vice president, threatened to withhold $1 billion in loan guarantees from Ukraine unless Shokin was fired. Many critics in Ukraine and the West had accused Shokin of being soft on corruption, but he also had been leading an investigation into Burisma's owner.

Fox News reported on the Biden controversy in April. The New York Times published a lengthy story on the matter in May. But, the controversy flew largely under the radar until last week. While the heat has been on Trump over whether he pressured Ukraine to investigate the Bidens, that firestorm has prompted multiple news outlets to revisit the original Biden controversy in order to provide context.

Fox News’ Chad Pergram, Jason Donner, Jake Gibson, Ronn Blitzer and The Associated Press contributed to this report.