Trump began Sunday morning by criticizing the special counsel on Twitter, one day after his lawyer issued a statement saying he prays for the Justice Department to end Mueller's investigation.

Republicans strongly cautioned the President and his team to let Mueller do his work.

Here are their key quotes:

Flake

Arizona Republican Sen. Jeff Flake said Sunday on CNN's "State of the Union" that he expects his colleagues in Congress, including GOP leadership, to push back on the President's comments and any potential move to force the end of the probe.

"I mean, talking to my colleagues all along it was, you know, once he goes after Mueller, then we'll take action," Flake said.

He likewise parted with Trump's triumphant assessment of Attorney General Jeff Sessions' firing of former FBI Deputy Director Andrew McCabe late Friday, saying that, counter to Trump's take, the dismissal of McCabe, who was ousted a little over 24 hours before he was to retire, "was a horrible day for democracy."

Ryan

AshLee Strong, a spokeswoman for House Speaker Paul Ryan, issued a statement on Sunday when asked for a reaction to the President's attacks on the Mueller probe.

"As the Speaker has always said, Mr. Mueller and his team should be able to do their job," Strong said.

When asked, Strong did not comment directly on whether Congress should advance legislation to protect Mueller.

Graham

South Carolina GOP Sen. Lindsey Graham said he continues to believe any attempt to fire Mueller would be catastrophic for Trump.

"If he tried to do that, that would be the beginning of the end of his presidency," Graham said on CNN's "State of the Union."

He went on to pledge to do his part to maintain the independence of Mueller's investigation. Graham also said the Senate Judiciary Committee should conduct a public hearing on the firing of McCabe for the sake of transparency.

"I think we owe it to the average American to have a hearing in the Judiciary Committee where Mr. Sessions, Attorney General Sessions, comes forward with whatever documentation he has about the firing, and give Mr. McCabe a chance to defend himself," Graham said.

Grassley

Taylor Foy, a spokesman for Senate Judiciary Committee Chuck Grassley, responded later Sunday to Graham's call for a hearing, saying Grassley's staff requested documents from the inspector general or FBI office of professional responsibility "that establish the factual basis for recommendations made regarding McCabe" and anticipated the release of the inspector general's report.

"The committee will be in a good position to hear testimony from witnesses once that independent review is published," the statement read.

And asked about legislation to protect Mueller, Foy reiterated Grassley's previous statements saying the "special counsel's investigation should be allowed to continue uninterrupted."

Gowdy

House Oversight Chairman Trey Gowdy, a South Carolina Republican, likewise vouched for Mueller and took issue with attacks on the probe from Dowd and Trump.

"I think the President's attorney frankly does him a disservice when he says that, and when he frames the investigation that way," Gowdy said on "Fox News Sunday."

He said later, "If you have an innocent client, Mr. Dowd, act like it."

The outgoing Republican did not mince words about McCabe either, saying the former top FBI official "undercut his credibility all by himself."

Gowdy, himself a former federal prosecutor, noted the FBI's own internal recommendation for the dismissal.

"The FBI is who recommended that he be fired," Gowdy said. "It wasn't crazy House Republicans, and it wasn't the Trump administration. It was his own fellow bureau agents."

Paul

Asked how he would respond to a potential attempt to dismiss Mueller, Kentucky Republican Sen. Rand Paul, also on CNN's "State of the Union," said he opposed special prosecutors in general.

"I've said all along I don't like special prosecutors," Paul said. "I think they have too much power and too much power to go far afield of the question."

Pressed on the issue, Paul said he would not "advocate" for Trump to try to force Mueller out, just as he "would have never advocated for the appointment of a special prosecutor."

"The power is so unlimited that it's worrisome," Paul said.

Rubio

Florida GOP Sen. Marco Rubio said he did not like the way McCabe's firing was handled and that appropriate action could have come after the release of a report from the Justice Department inspector general.

"He should've been allowed to finish through the weekend," Rubio said on NBC's "Meet the Press."

Rubio, who sits on the Senate Intelligence Committee, vouched for Mueller's investigation later in the interview when asked about Trump's tweet Saturday night that the probe "should never have been started."

"I remain confident that the special counsel is going to conduct a probe that is fair and thorough and is going to arrive at the truth and is not going to go down rabbit holes that are not places that we need to be going," Rubio said.

Lankford

Oklahoma Republican Sen. James Lankford, also a member of the Senate Intelligence Committee, said on ABC's "This Week" that he does not think Trump will move to oust Mueller despite Dowd's comments.

"I don't see the President firing him," Lankford said. "I think the White House has said 10 times, maybe more, that they're not going to fire Robert Mueller, they want him to be able to finish the investigation."

Democrats

Senate Minority Leader Chuck Schumer and California Democratic Rep. Adam Schiff both called on their Republican colleagues to temper the President.

Schumer said in a statement that Trump is "floating trial balloons" to derail the investigation and said Republicans "have an obligation" to establish that Mueller's firing would be a red line.

Schiff, on ABC's "This Week," said he would hope if Trump tries to oust Mueller, then the House would pass a law reinstating the former FBI director as an independent counsel.

"Members need to speak out now, don't wait for the crisis," he said.

On McCabe, Schiff said the firing might have been justified, but that Trump's repeated attacks on McCabe in the lead-up to the firing could belie an inappropriate motivation behind the move.

Senate Minority Whip Dick Durbin, of Illinois, said on "Fox News Sunday" that he agreed with Gowdy's remarks, adding that "any effort by the President or his counsel to try to stop this investigation needs to be resisted on a bipartisan basis."

Mirroring Schiff's comments, Durbin said any attempt to fire Mueller would be a "constitutional crisis" and that "it would be incumbent on Congress, on a bipartisan basis, to use the tools at its disposal."

He referenced legislation that would aim to protect the special counsel from Trump.

"We ought to pass those bills now," Durbin said. "This President is engaged in desperate and reckless conduct to intimidate the law enforcement agencies in this country and to try to stop the special counsel."