Washington (CNN) For months, President Trump has been obsessed -- publicly and privately -- with clearing his name in relation to the ongoing investigation into Russia's meddling in the 2016 election and potential collusion with members of his campaign.

Trump, we know now, repeatedly asked then-FBI Director James Comey whether he, personally, was under investigation. On three occasions, Comey said he was not.

"I know I'm not under investigation," Trump told NBC's Lester Holt in a May 11 interview that came just two days after Trump had fired Comey over, according to the President , the FBI director's handling of the Russia investigation. "I'm not talking about campaigns. I'm not talking about anything else," Trump added. "I'm not under investigation."

That isn't true anymore, according to reporting by The Washington Post on Wednesday night . That report makes clear that three senior intelligence officers -- Director of National Intelligence Dan Coats, National Security Agency Director Mike Rogers and and former NSA deputy director Richard Ledgett -- are being interviewed this week by special counsel Bob Mueller as he looks into whether Trump obstructed justice in the Russia case.

A source familiar with the matter later told CNN that Mueller's investigators have asked for information and will talk to Coats and Rogers.

"Trump had received private assurances from then-FBI Director James B. Comey starting in January that he was not personally under investigation. Officials say that changed shortly after Comey's firing."

Trump wasn't under investigation personally prior to Comey's firing on May 9. But he is now, according to the Post.

That's absolutely huge -- for several reasons.

First, it makes it virtually impossible for the President and his administration to dismiss this probe as a sideshow or small potatoes or a distraction somehow created by the biased media. (That doesn't mean they won't do exactly that, of course.) We are now talking about the President of the United States being investigated for possibly obstructing justice in relation to a criminal probe about a foreign government meddling in our elections for the purpose of defeating his Democratic opponent.

Consider that paragraph. And consider we are less than 150 days into Trump's presidency and this -- an investigation by a special counsel who also happens to be the former FBI director -- is where he finds himself.

Second, it suggests that not only is the special counsel's investigation reaching upward in the White House but that is also broadening out from simply an attempt to answer the question of the breadth of Russia's hacking and whether it caught up any Trump officials in it.

Looking into whether Trump obstructed justice means that Mueller is also examining the circumstances surrounding Comey's firing, which was obviously not part of the original federal probe led by Comey when he still had a job as FBI director.

As the Post story notes:

"The interviews (with Rogers, Coats and Ledgett) suggest that Mueller sees the question of attempted obstruction of justice as more than just a 'he said, he said' dispute between the President and the fired FBI director, an official said."

That's critical given that Comey's sworn testimony regarding the pressure put on him by Trump to leave off an investigation into deposed national security adviser Michael Flynn runs directly counter to Trump's assertions about their conversations. Trump -- while not under oath, it's worth noting -- has insisted flatly that he had never urged Comey to slow or stop the Flynn investigation.

Trump appeared unbowed by the new revelations.

"They made up a phony collusion with the Russians story, found zero proof, so now they go for obstruction of justice on the phony story. Nice," he tweeted Thursday morning. He soon added : "You are witnessing the single greatest WITCH HUNT in American political history - led by some very bad and conflicted people! #MAGA"

None of the above makes Trump guilty. But, what it does is take this special counsel investigation all the way into the Oval Office -- a place where it hasn't gone before. And it also suggests that Mueller isn't narrowing the scope of the investigation he took over on May 18 , he's widening it.

All of which makes Trump's efforts to belittle the investigation and move past it that much more difficult.