Where things stand with special counsel Mueller's Russia probe

Robert Mueller is conducting what is generally called a preliminary inquiry.

— -- Department of Justice–appointed special counsel Robert Mueller is conducting what is generally called a preliminary inquiry into possible obstruction of justice involving President Donald Trump, as it pertains to his broader investigation into Russian meddling in the U.S. presidential election.

At some point, Mueller may wish to interview FBI senior leadership about their meetings with Comey regarding Trump, though it's unclear if this has already taken place.

A full-scale investigation has not yet been launched, although preliminary work is clearly being done, according to sources familiar with the process.

An assessment of evidence and circumstances will be completed before a final decision is made to launch an investigation of the president of the United States regarding potential obstruction of justice.

Comey said under oath during his much-anticipated Senate hearing earlier this month that he believes he was fired because of the Russia investigation.

"Guess I don’t know for sure. I believe the — I take the president at his word, that I was fired because of the Russia investigation. Something about the way I was conducting it, the president felt, created pressure on him that he wanted to relieve,” Comey told the Senate Select Intelligence Committee.

Any kind of alleged effort to interfere in an investigation could potentially lead to an obstruction of justice investigation targeting the president and his aides.

The deputy attorney general could become a witness if the circumstances of Comey’s firing are considered part of an obstruction investigation.

To indicate that a full scale investigation has been launched, all eyes will be on Rosenstein's actions, as well as evidence of a grand jury subpoenaing key White House aides with a focus on Trump. Another key will be Mueller's assessment of Comey allegation that Trump tried to get him to stop the investigation of former National Security Advisor Michael Flynn.