WASHINGTON — The disclosure that Russia’s ambassador to the United States spoke twice with Attorney General Jeff Sessions last year, even though Mr. Sessions testified at his January confirmation hearing that he “did not have communications with the Russians,” has set off a new round of political furor in Washington, this time with legal overtones.

After Republicans began joining Democrats on Thursday in calling upon Mr. Sessions to recuse himself from overseeing any criminal investigation related to Russian meddling in the 2016 election, the attorney general announced that he would step aside from any current or future cases related to the campaign. As a senator, Mr. Sessions was a top campaign adviser to President Trump.

But some Democrats called for giving the investigation even greater independence. Others accused Mr. Sessions of lying under oath and called for his resignation and a criminal investigation. The developments have heightened interest in several related legal issues.

What does it mean for the attorney general to recuse himself?

Generally, United States attorneys directly oversee criminal investigations. In a case that raises politically sensitive issues, the attorney general would normally be briefed on proposed major decisions — like whether to subpoena a high-profile witness or bring charges — and could overrule them. By recusing himself now, Mr. Sessions is responding to concerns that exercising that role, in light of his ties to the Trump campaign, would call into question the impartiality of the justice system.