President Trump announced Sunday that he had selected Texas Republican congressman John Ratcliffe to replace Dan Coats as Director of National Intelligence when the latter steps down from the post next month.

That sets up what looks to be a brutal confirmation battle, with Democratic critics already arguing that the president choose Ratcliffe less for his experience and more for his loyalty to the White House.

The 53-year-old Ratcliffe, who spent eight years as the mayor of the small town of Heath, has been a fierce defender of Trump’s policies and agenda, becoming one of the most vocal critics of former Special Counsel Robert Mueller’s investigation into Russian interference in the 2016 election and any collusion with the Trump campaign.

The congressman made headlines last week when he grilled Mueller during a hearing on Capitol Hill.

"You wrote 180 pages about decisions that weren’t reached, about potential crimes that weren’t charged or decided," Ratcliffe said to Mueller. "Respectfully, by doing that, you managed to violate every principle and the most sacred of traditions about prosecutors."

He added: "It was not the special counsel’s job to conclusively determine Donald Trump’s innocence or to exonerate him because the bedrock principle of our justice system is a presumption of innocence.”

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Ratcliffe has also argued that the administration of former President Barack Obama committed crimes in connection with events that preceded the start of the Mueller investigation and has lobbied for an investigation into the matter.

"I'm not going to accuse any specific person of any specific crime," Ratcliffe said on Fox News' “Sunday Morning Futures.” "I just want there to be a fair process to get there. What I do know, as a former federal prosecutor, is, it does appear that there were crimes committed during the Obama administration."

The Texas lawmaker has also sided with Trump when it comes to immigration, voting in January against the appropriations bill to end a government shutdown because it did not include all the funding for the president’s proposed border wall.

Before joining the House in 2015, Ratcliffe served as the mayor of Heath– a town of about 9,000 people – for eight years, and lives there with his wife and two daughters. He has also worked as a U.S. Attorney and federal terrorism prosecutor, and was an aide to Sen. Mitt Romney, R-Utah, during his 2012 presidential campaign.

In the House, Ratcliffe has served on the Intelligence, Homeland Security, Judiciary and Ethics Committees. In 2016, the Heritage Foundation ranked Ratcliffe as the most conservative Texas legislator in Congress and second-most conservative legislator in the country.

While Ratcliffe’s loyalty and alignment with Trump are not in question, his confirmation before the Senate is still very much up in the air as Democrats question his credentials to oversee one of the most important and sensitive arenas in the U.S. government, and one that has traditionally been seen as non-partisan.

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"It's clear that Rep. Ratcliffe was selected because he exhibited blind loyalty to President Trump with his demagogic questioning of former Special Counsel Robert Mueller," Senate Minority Leader Chuck Schumer, D-N.Y., said in a statement. "If Senate Republicans elevate such a partisan player to a position that requires intelligence expertise and non-partisanship, it would be a big mistake."

Sen. Gary Peters, D-Mich., echoed his Democratic colleague, telling CNN that he’s “not sure [Ratcliffe’s] qualified for the job.”

“The president doesn't want people to challenge him, and when you think about an intelligence director, you want independent advice,” Peters added. “You want to have the best available intelligence to make decisions that are based on facts and reality. That is not something our current president wants.”

Most Republicans have yet to show their hands when it comes to how they will vote on Ratcliffe’s confirmation, with many issuing statements praising the work of Coats while failing to mention Ratcliffe at all.

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Senate Majority Leader Mitch McConnell praised Coats in a statement, calling him “a man who took such a deliberate, thoughtful, and unbiased approach.”

“This was especially true during a time of growing international tension. Under Director Coats’ leadership, our agencies have gotten a better handle on the malign behavior of Russia, China, and other adversaries such as Iran and North Korea,” McConnell added. “Director Coats pushed for greater coordination in how the community approaches some of its hardest, most sensitive collection targets.”

Sen. Susan Collins, R-Maine, who has a history of criticizing President Trump, also gave no hint of of her thoughts on Ratcliffe. In a tweet, Collins only praised Coats as “one of the finest public servants I have ever known.”

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She added: “He led the intelligence community with integrity and skill, and his departure is a huge loss to our country."