The former White House aide said the Kremlin had been "mucking around" in elections for decades.
Sixty percent of American voters feel the investigation is being conducted fairly, a poll shows.
Miller had not previously been identified in documents related to the investigation by special prosecutor Robert Mueller.
Republican lawmaker says Mueller "must step down immediately" because of ties to the Obama administration.
Among those who felt President Donald Trump likely committed a crime, 19 percent believed there was solid evidence
The president's base has lined up behind him amid the Russia probe.
Eric Trump's fundraising email has the subject line "Still standing."
The Clinton campaign and DNC helped finance the Steele dossier, but important elements of the document have panned out.
Comey may simply have gone to Iowa to attend a family birthday dinner.
The former presidential nominee said that if she had been elected she'd have called for an independent commission to "get to the bottom of it."
Key homeland security posts remain unfilled on the anniversary of warning of Russian interference in the 2016 presidential election.
The two documents concern emails sent between a Trump associate and Russian officials.
A report from the U.K.-based Rusi think tank explains reasons that could motivate the president to use force against Pyongyang.
Senator Diane Feinstein said the testimony would come soon.
Former campaign adviser struggles to pay for legal defense team during Russia probe.
Clinton made the remarks despite Comey's decision to reopen the FBI probe into her private email server during the campaign.
Comey confidant Ben Wittes said comments made by Sarah Huckabee Sanders amounted to a "disgusting abuse."