A top GOP senator said Tuesday night that President Trump's firing of FBI Director James Comey raises questions about the ongoing investigation into Russia.

"It is essential that ongoing investigations are fulsome and free of political interference until their completion," Sen. Bob Corker, R-Tenn., said soon after news of Comey's firing surfaced.

Corker said the removal of Comey now, when the FBI is investigating the Trump campaign's connections to Russian officials, "will raise questions."

However, he did say that Deputy Attorney General Rod Rosenstein, who was confirmed several weeks ago, gave a thorough case for Comey's removal.

Rosenstein wrote in a memo to Attorney General Jeff Sessions that Comey's press conference last summer recommending no charges for Hillary Clinton over her private e-mail server "ignored longstanding principle."

"We do not hold press conferences to release derogatory information about the subject of a declined criminal investigation," Rosenstein wrote.

Sessions, who recused himself from the Russia investigation because of his work for the Trump campaign, agreed with Rosenstein's recommendation to dump Comey.