(CNN) Democrats are ratcheting up their vows to stop Rep. John Ratcliffe from being confirmed as the next director of national intelligence amid questions about whether the Texas Republican exaggerated his resume as a federal prosecutor working on terrorism cases.

"This is one more item that raises enormous red flags to me," Virginia Sen. Mark Warner, the top Democrat on the Senate Intelligence Committee, told CNN. "Director Coats was willing to speak truth to power. I've seen no evidence from what I've read or seen about Mr. Ratcliffe, that he'll bring that same level of independence. And what I fear is that the deeper we get into the Trump administration, the more this president wants 'yes-men.'"

Senate Democrats are gearing up for a confirmation fight following President Donald Trump's choice of Ratcliffe to replace Dan Coats as the head of the US intelligence community, saying he thought Ratcliffe would "rein in" the intelligence agencies that the President feels "have run amok."

When Trump said he would nominate Ratcliffe, Democrats argued that the pick was too political, pointing to Ratcliffe's vocal criticisms of special counsel Robert Mueller's investigation that align with the President's. Ratcliffe's played a leading role in the GOP-led investigation into the Justice Department and FBI's handling of the Russia investigation, and he accused them of abusing their authority investigating the President's advisers in 2016. Ratcliffe has also called for probing the actions taken in the Russia investigation by the intelligence community that he would lead if confirmed.

Now Democrats are raising new questions about Ratcliffe's resume as a federal terrorism prosecutor, a significant part of his biography given his short, seven-month tenure on the House Intelligence Committee. Ratcliffe claimed as a US attorney and federal terrorism prosecutor he "put terrorists in prison," but his office has not provided names of any terrorism suspects sent to prison as a result of his prosecutorial work.

That has Democrats vowing to stop Ratcliffe's confirmation.

"I will pull out all the stops to make sure someone like this -- I think will do so much damage to the credibility of the American intelligence community at a critical time for our country -- I will do everything I can to stop this nomination," said Sen. Ron Wyden, an Oregon Democrat on the Senate Intelligence Committee.

"One of the reasons it's so troubling is that his record is so flimsy in the first place," Wyden added. "And the limited amount we know is, to some extent, either inflated or made up, to some measure."

Sen. Angus King, a Maine independent who caucuses with Democrats, said the matter was "of serious concern."

"I think it's important to get to the bottom of it. I've seen or heard the ad where he cited his work, and I've also seen the reports that it was in fact exaggerated," King said. "That will, I'm sure, be considered by the committee."

Senate Minority Leader Chuck Schumer on Thursday called Ratcliffe "extremely unqualified in every way," signaling Democrats will try to defeat his nomination.

"If we don't have a DNI who speaks truth to power — who first is able to cull the facts and come up with an unbiased view of what they say, and in an unvarnished way can tell the President — we are in a more dangerous world than they would have been," Schumer said. "I can hardly think of a worse choice than him -- padding resume, or not."

What GOP senators say

Senate Intelligence Chairman Richard Burr, a North Carolina Republican, declined to address questions about Ratcliffe's resume on Thursday, saying he would do so after his committee formally received the Texas Republican's nomination. "You're asking me to comment on a news story of somebody that's not been nominated," Burr said. "When he's nominated, and we do an investigation, I'll be happy to comment on what I think his qualifications are."

Earlier this week, Burr said that once he received the paperwork from the White House, he would "work aggressively" to confirm Ratcliffe.

A spokeswoman for Ratcliffe said Justice Department records would "confirm that as both Chief of Anti-Terrorism and National Security for the Eastern District of Texas from 2004-2008, John Ratcliffe opened, managed and supervised numerous domestic and international terrorism related cases."

CNN's initial search of court records did not find any terrorism cases he was listed as prosecuting. The Justice Department has not commented.

Ratcliffe's office also cited his association with a terrorism-related case that was brought by federal prosecutors in another Texas district involving the Holy Land Foundation for Relief and Development and five former leaders who were accused of funneling money to the Palestinian militant group Hamas. The first time the case went to trial, it ended with a hung jury.

Republicans on the Senate Intelligence Committee said they were not familiar with the details of Ratcliffe's record as a prosecutor and declined to comment on news reports about his resume.

"I don't know anything about that," said Missouri GOP Sen. Roy Blunt, an intelligence panel member.

"His resume is going to be looked at. ... I'm going to wait for him to come, submit his documents and go from there," said Sen. Marco Rubio, a Florida Republican on the Intelligence Committee. "I've talked to him a bunch, I've known him, but I've never had a conversation with him about the intelligence community. I'll know more about him in the next few weeks."

Sen. Susan Collins, a Maine Republican, said she co-authored the legislation creating the office of the director of national intelligence and she cared deeply about appointing the right person to lead the intelligence community. But she said she hadn't heard much yet about Ratcliffe.

"I haven't heard that," Collins said when asked about questions over his resume. "I've yet to meet him and know very little about him. Frankly his name was unknown to me prior of my reading of the transcripts of hearings."

Of more immediate concern for the committee is who Trump places in the role of acting director of national intelligence with Coats departing on August 15. Burr, Warner and other senators have argued for Deputy Director Sue Gordon to assume the acting role, but sources told CNN this week there was an active search for other candidates to take the position until Ratcliffe is confirmed.

Burr said on Thursday that the Trump administration was required by law to place Gordon in the position.

"The statute is very clear," he said. "The principal deputy takes over as acting."

Asked what happens if the White House picks someone else, Burr argued they could not: "It's a legal issue. ... Read the statute. I know what my interpretation is."