Here's why Jeff Session's Senate testimony is a big deal

The Senate Intelligence Committee called on Attorney General Jeff Sessions to testify in an open hearing on Tuesday, and the event is expected to be another must-see installment in the Russia investigation saga.

The committee is investigating President Donald Trump's associates' ties to Russia, and whether Trump's team colluded with the Kremlin's meddling in the 2016 election.

Sessions, who oversees the FBI as head of the Department of Justice, recused himself from the bureau's Trump-Russia investigation after previously undisclosed meetings he had with Russian ambassador Sergey Kislyak came to light.

On Tuesday, senators are expected to ask Sessions about former FBI Director James Comey's June 8 testimony, when he talked about his interactions with Trump and the president's move to fire him in May. They will also likely bring up his meetings with Russian officials.

Here's a primer on Sessions and his Senate testimony, which begins at 2:30 ET on Tuesday:

Who is he?

Sessions, who was a junior senator from Alabama before becoming US attorney general, was one of Trump's earliest congressional supporters.

Before joining the Senate, he was a US attorney and the attorney general of Alabama. Sessions is a staunch opponent to immigration reform, and has ushered in many of Trump's strict immigration policies, including the travel bans that are currently held up in the courts.

Sessions' consideration for a Cabinet position revived allegations of racism that jeopardized his chance to become a federal district court judge in 1986, when a prosecutor testified that Sessions once called the NAACP and the ACLU "un-American."

Senate Minority Leader Chuck Schumer said he was "very concerned" about Sessions' civil rights record, a sentiment that other liberals echoed. Schumer and 46 other Democrats voted against his confirmation in February.

Many conservatives, meanwhile, applauded Trump's choice, with 52 Republican senators and one Democrat voting to confirm him.

Why did Sessions recuse himself?

During his confirmation hearing in February, Sessions said he didn't have contact with "the Russians" during the campaign.

Senator Al Franken of Minnesota asked: "If there is any evidence that anyone affiliated with the Trump campaign communicated with the Russian government in the course of this campaign, what will you do?"

"Sen. Franken, I'm not aware of any of those activities," Sessions responded. "I have been called a surrogate at a time or two in that campaign and I did not have communications with the Russians, and I'm unable to comment on it."

But in March, the Wall Street Journal and others reported that Sessions met with ambassador Kislyak at least twice during the 2016 campaign - once at an event timed to the Republican National Convention and again in September.

Lawmakers have publicly wondered about a possible third meeting at an event where both Sessions and Kislyak were both spotted in April 2016. Then-candidate Trump was giving a foreign policy speech at the Mayflower Hotel in Washington.

Senate Democrats have raised the possibility that Sessions and Kislyak could have met there, though Justice Department officials say there were no private encounters or side meetings. Comey testified during a closed Senate hearing last week that intercepted Russian-to-Russian communications indicated that Sessions met with Kislyak at the event, though the intel was unverified, CNN reported last week.

After cries from both sides of the aisle for Sessions to recuse himself from the FBI's Trump-Russia investigation, he stepped aside from "any matters related in any way to the campaigns for President of the United States" on March 2.

What will he say?

On Tuesday, Sessions is expected to discredit Comey, and claim the former FBI director misrepresented an interaction that he and Trump had when he testified on Thursday.

Comey said in his sworn testimony that he felt Trump was trying to pressure him to drop the FBI investigation into former national security adviser Michael Flynn. Comey testified that when he approached Sessions about the one-on-one meeting with the president, the attorney general remained silent.

"In light of reports regarding Mr. Comey's recent testimony before the Senate Select Committee on Intelligence, it is important that I have an opportunity to address these matters in the appropriate forum," Sessions said in a letter on Saturday confirming that he would appear before the committee.

Democratic Senator Jack Reed of Rhode Island said on Sunday that he would grill Sessions on his involvement with Trump's decision to fire Comey.

Sessions will get his chance to tell his side of the story on Tuesday. He could also clarify why he met with Russian officials.

Why does it matter?

Sessions' testimony shows that the Senate Intelligence Committee Trump-Russia investigation continues, as a parallel investigation in the House has lost steam. The FBI is still conducting its investigation, as well.

In his blockbuster testimony, Comey also said that Trump asked Sessions to leave the room before the president implored his FBI director to drop the investigation into Flynn's contacts with Russian officials. Senators could ask Sessions about his recollection of that incident, and his opinion of that testimony.

Senators could also probe whether Sessions was following through with his pledge to recuse himself from the Trump-Russia investigation, and whether Trump plans to try to fire Special Counsel Robert Mueller, who was brought in to lead the investigation in order to keep it independent from the administration.

What Sessions says Tuesday could help senators get to the bottom of whether the Trump campaign colluded with the Russians, and whether the Kremlin has undue influence over his administration.