Top Republicans are moving to block a Senate inquiry into the Trump justice department’s secret seizure of data from Democrats to hunt down leaks of classified information, fearing a close investigation could damage the former president.

Trump, who is facing a mounting crisis of legal problems and political criticism, still wields huge power among Republicans, and has hinted recently at a return run for the White House.

In fiery remarks, the Republican Senate minority leader, Mitch McConnell, criticized the rapidly expanding congressional inquiries as unnecessary and accused Democrats of embarking on “politically motivated investigations”.

“I am confident that the existing inquiry will uncover the truth,” said McConnell. “There is no need for a partisan circus here in Congress.”

The forceful pushback from McConnell shows his alarm about the latest aggressive move by Democrats to engage in retrospective oversight that could expose Trump for misusing the vast power of the federal government to pursue his political enemies.

It also means Republicans are certain to lock arms to block subpoenas against Trump justice department officials, including former attorneys general Bill Barr and Jeff Sessions. Democrats need at least one Republican member for subpoenas because of the even split between Democrats and Republicans on the panel.

Chuck Grassley, the top Republican on the Senate judiciary committee, suggested he would offer no such support. “Investigations into members of Congress and staff are nothing new, especially for classified leaks,” he said.