Donald Trump has denied new claims linking Attorney General Jeff Sessions with Moscow. US media meanwhile reported that Vice President Mike Pence used a private email account for "sensitive matters."
Responding to accusations about ties between his aides and Moscow, US President Donald Trump took to Twitter on Friday, where he called for "an immediate investigation" into Senate Minority Leader Charles Schumer's own ties to Russian President Vladimir Putin.
Alongside a tweet in which he called the Democrat "a total hypocrite," Trump posted a photo of Schumer as he met with Putin in New York in 2003.
Schumer responded on Twitter soon after, stating that he would "happily talk" under oath about his meeting with Putin, which took place "in full view of press and public" - before challenging Trump to do the same.
The unfolding drama in the White House on Friday came as US media also reported that US Vice President Mike Pence used a private email account for matters of public business while still in office as governor of Indiana.
Emails obtained by the "Indianapolis Star" newspaper showed that Pence used the private account - which the paper reported was hacked last summer - to at times discuss "sensitive matters" and "homeland security issues."
Pence defends use of private email account
The Star, which obtained the emails in a public records request, said that in response to its investigation Pence's office confirmed that the vice president "maintained a state email account and a personal account."
'Absurd' comparison with Clinton
Although Indiana law does not prohibit public officials from using personal email, it does generally require that messages connected to official business are kept for public information purposes.
Pence's office told the "Indianapolis Star" that his campaign had taken steps to allow outside counsel to transfer personal emails dealing with public business to the state.
Pence's spokesman Marc Lotter, however, described the comparison with Clinton as "absurd" as the Democrat had set up a private server in her home at the start of her tenure at the State Department. Unlike Clinton, Pence did not handle any classified material as Indiana's governor, Lotter said.