Washington (CNN) The Senate intelligence committee hearing of former FBI Director James Comey was already going to be a blockbuster before it even started -- with Comey stating in pre-written testimony Wednesday that President Donald Trump urged him to drop his investigation into former national security adviser Michael Flynn.

But while it may seem that Comey's decision to release his testimony a day early actually upstages his own appearance, in reality he gave senators a running start to come up with more pointed, probing questions for him when they all take the national stage Thursday morning.

Here are five things to watch for Thursday when the hearing kicks off at 10 a.m. ET:

1. The former FBI director will testify under oath that the President asked him to drop an investigation into one of his top allies

It's impossible to lose sight of the most important items to emerge from the Russia investigations thus far: Trump asked Comey to stop investigating Flynn.

If you're a Democrat, that sounds like obstruction of justice (and possible grounds for impeachment .) If you're a Republican, it may sound like a political novice asking his aide to help one of his friends. But it is one of the most important, and prominent, developments in the sprawling web of the Russia investigations.

And Comey is poised Thursday to take that fact out of the realm of anonymous (and accurate) reporting and formally place it in the record publicly, under threat of perjury if it's not true.

Comey, in detail, relays how Trump asked all of his top advisers to leave a February 14 meeting in the Oval Office -- one by one -- until he was alone with Comey. After explaining that he wanted to talk about Flynn, Trump said he wanted Comey to "let this go."

Comey writes, "He then said, 'I hope you can see your way clear to letting this go, to letting Flynn go. He is a good guy. I hope you can let this go.'"

2. But is it obstruction of justice?

Watch for a battle between Democrats and Republicans over how to characterize Trump's request of Comey -- as well as Trump's other requests, like his repeatedly asking Comey for his loyalty.

Democrats on the Senate Intelligence Committee were mum Tuesday, as they left a classified briefing after Comey's testimony went public. But their counterparts on the House Russia investigation clearly thought the testimony could prove obstruction of justice by Trump.

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Rep. Adam Schiff, the top Democrat on the House probe, said he wants to know if Trump's request for loyalty and that Comey drop his Flynn investigation ultimately led to Comey's firing.

"Congress must now determine whether the Director's refusal to do either -- or any other motivation to interfere with or obstruct any part of the Russia investigation -- led ultimately to Comey's firing," Schiff said in a statement.

Senate intelligence committee Chairman Richad Burr, who has taken a firm and methodical stance leading the Russia investigation, said Tuesday that his quick reading of Comey's testimony showed no wrongdoing, but that could change.

"I don't think from what I've read there's any evidence of wrongdoing," Burr told reporters. "I will match that against his verbal testimony and weigh that against the evidence to date."

3. 'Trump was right'

That was the comment from the Republican National Committee after Comey's testimony was released and, for one very key point, it is dead on: Trump is correct that Comey told him multiple times the FBI was not investigating him personally.

The first (and only) comment from Trump's newly appointed spokesman and lawyer on all things involving Russia, Marc Kasowitz, hammered home that they feel "totally vindicated."

"The President is pleased that Mr. Comey has finally publicly confirmed his private reports that the President was not under investigation in any Russian probe. The President feels completely and totally vindicated. He is eager to continue to move forward with his agenda," Kasowitz said in a statement.

That fact is only one tree in a Siberian forest that is filled with bad news for Trump. But it's still a glimmer of good news in the story that has cast an omnipresent cloud over Trump's administration.

4. Can senators extract more from Comey in public?

Comey is a veteran at testifying before Congress -- having filled the role now held by Deputy Attorney General Rod Rosenstein more than a decade ago and testified regularly as the FBI director. He has frequently offered up important nuggets -- but also has a plethora of ways to say, ever so politely, that he will not answer a question.

Sen. Dianne Feinstein, a veteran member of the Senate Intelligence Committee and former chairwoman of the panel, hinted at this in an interview with CNN's Dana Bash Tuesday.

"It's seven pages of very fine print and what it describes is a professional law enforcement person, who is Jim Comey, who comes up against a president who knows no limits in terms of a proper relationship," Feinstein said Tuesday of Comey's testimony . "It was really pretty remarkable that he put this in writing (the night before the hearing.) We will see how much he's prepared to do verbally."

Sen. Mark Warner, the top Democrat on the committee, spent Wednesday afternoon and early evening preparing his questions for Comey. Excerpts from his opening statement were released Thursday morning.

"This is not how a President of the United States behaves," Warner is expected to say, referring to Comey's testimony. "Regardless of the outcome of our investigation into those Russia links, Director Comey's firing and his testimony raise separate and troubling questions that we must get to the bottom of."

5. Other Comey surprises

Comey's recent hearings on the Hill -- before he was fired -- had offered some very stunning revelations.

On March 20, he revealed publicly that the FBI had been investigating the Trump campaign since last July -- in a House hearing which prefaced the House investigation almost spiraling out of control.

And just a week before he was fired -- Comey told the Senate Judiciary Committee that he decided to publicly announce his findings in the Clinton email investigation after watching Bill Clinton board a plane with then-Attorney General Loretta Lynch. (However, later reporting revealed that Comey actually acted based on Russian misinformation alleging collusion between the Clinton campaign and the Obama Justice Department.)

In short: Comey's public hearings tend to be explosive news-fests.

He already uncorked a few big surprises in his testimony -- be on the lookout for more Thursday.