As House Democrats ramp up their investigations of President Trump, Fox News senior political analyst Brit Hume said Monday it's not a coincidence that it's happening shortly before Special Counsel Robert Mueller's Russia probe is expected to end. 

House Judiciary Committee Chairman Jerry Nadler (D-N.Y.) announced the committee served document requests to 81 agencies, entities and individuals, as part of a new probe into "alleged obstruction of justice, public corruption, and other abuses of power by President Trump."

On Sunday, Nadler declared in a TV interview that it was "clear" Trump had obstructed justice. 

Hume said Nadler would be moving straight to impeachment proceedings if he possessed evidence of obstruction of justice.

"There doesn't appear to be many people now who any longer think [Mueller] will come up with some kind of conspiracy theory related to collusion by the Trump campaign with the Russians. ... So the search is on for something else really. They may try to figure out some kind of obstruction of justice charge, but it appears they are moving away from collusion," Hume observed.

Hume said Mueller is likely to offer a report on whether the Trump campaign colluded with Russia, since that was a key part of his appointment. 

He said it's unclear how the American public will respond to a slew of new investigations if Mueller does not agree that Trump "was greatly aided by the Russians in a grand conspiracy to throw the election."

Hume said to move forward on impeachment, Democrats will have to be able to show crimes committed by the president while in office, especially if Mueller "doesn't come up with something big."

He said Democrats will have a political calculation to make on whether to keep multiple investigations going or to focus on legislation ahead of the 2020 election. 

"Even if they don't pass things and get them signed, if they pass a lot of bills that the president has to veto or get blocked in the Senate, those become issues the Democrats can run on as a way to get their candidates and their presidential candidate elected," he explained.

Watch the "Special Report" analysis above.

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