Trump officially nominated Tillerson today. That will raise red flags in Congress.

UPDATE 5:36 a.m. EST 12/13:

President-elect Donald Trump will officially nominate Rex Tillerson, CEO of ExxonMobil, as Secretary of State Tuesday, Reuters reports. 

Tillerson was backed by former secretaries of state James Baker and Condoleeza Rice  and former Defense Secretary Robert Gates, Reuters reports. 

Reuters also reports Trump has selected former Texas Gov. Rick Perry as energy secretary, with an official announcement coming later.

Trump shared his announcement on Twitter.

WATCH  | Several of Donald Trump's Cabinet picks have caused a stir, but his latest candidate for Secretary of State is raising some big red flags in Congress. If Trump decides to nominate ExxonMobil CEO Rex Tillerson, he will be in for some intense deliberations in Congressional hearings. 

Trump breaking ranks with the GOP on Russia 

Several top Republicans have already expressed concern over Tillerson's ties to the Kremlin. The oil tycoon has worked extensively in Russia. In 2013, he received the Order of Friendship, one of the highest honors the Kremlin bestows on foreigners. 

Sen. John McCain, R-Ariz., has said he is concerned about reports of Tillerson's relationship with Putin, and said questions about that relationship would certainly come up n Senate hearings. 

Marco Rubio, who serves on the Senate Foreign Affairs Committee, blasted Tillerson.

The chairman of that committee just called Tillerson an "impressive" person.

Democrats are worried too 

Democrats are also worried about Tillerson's relationship with Putin's government, and have raised concerns over potential conflicts of interest that could influence his foreign policy decision. 

"We want to make sure that the Secretary of State is a person who represents America.  And once again, Russia is not our friend," said Sen. Ben Cardin, D-Maryland, who also serves on the Foreign Affairs Committee. That committee will conduct initial hearings if Trump decided to nominate Tillerson.

Conflicts of Interest 

Experts say Tillerson's oil ties could be an even bigger problem than his personal relationship with Putin. Tillerson will likely want to re-examine U.S. economic sanctions on Russia, imposed after the annexation of the Crimea.

"Exxon has already lost substantial amounts of money and will lose more if the sanctions stay in place," said Emma Ashford, a research fellow at the Cato institute. 

A debate on climate change 

Some Democrats have already signaled that they would use confirmation hearings to grill Tillerson on the Trump administration's denial of climate change. 

They could also use it as an opportunity to question Tillerson on reports that suggest Exxon has known for years that fossil fuels exacerbate climate change. 

"Everything is on the table when it comes to [Tillerson] testifying under oath," a Senate Democratic aide told POLITICO.

When will Trump make it official? 

Trump, who has said Tillerson is a "world-class guy," is expected to announce his nomination for Secretary of State later this week.

If he picks Tillerson, it will set him up for a long fight with Congress. Democrats alone don't have enough clout in the Senate to block Tillerson's nomination, but it would only take two or three Republicans to go against their party to make that happen.  

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