Former independent counsel Kenneth Starr on Monday urged the Senate to quickly clear President Donald Trump's name in its impeachment trial, saying the current proceedings could open the door to more presidential impeachments down the line.

Starr, a former judge on the U.S. Court of Appeals for the D.C. Circuit who oversaw the Clinton-era independent counsel probe, repeatedly referenced the impeachment proceedings against former President Bill Clinton that his office triggered.

Starr said the "common law" of presidential impeachments has set the way for impeachment to become a more frequently used political tool, instead of a rarely used constitutional check.

"Instead of a once-in-a-century phenomenon, which it had been, presidential impeachment has become a weapon to be wielded against one's political opponent," Starr told the Senate.

He acknowledged that the Clinton impeachment proceedings were widely criticized, but said the existence of a criminal violation—perjury—merited consideration by the Senate on whether to remove the president from office. Starr argued the same could not be said for Trump.

"The Senate in its wisdom would do well to guide the nation, as this world's greatest deliberative body, to return to our country's tradition of when presidential impeachment was truly a measure of last resort," Starr said.

Starr's was the first of several presentations set to be given by members of the president's legal defense team. The defense began Jan. 25, with the president's lawyer giving a two-hour overview of their case that Trump "did nothing wrong" by withholding of military aid from Ukraine, as he pushed for investigations into the Bidens.

The former independent counsel said he believed there should be an underlying crime in order to move forward with an impeachment proceeding, an argument that has been largely rejected by constitutional law scholars.

"Will law professors agree with this? No. But with all due respect to the academy, this is not an academic gathering," Starr said. "We're in court. We're not just in court, with all due respect to the chief justice and the Supreme Court of the United States. We're in democracy's ultimate court."

Starr also reiterated the Trump legal team's argument that the House should have gone to court to obtain more materials in its inquiry. That claim contradicts the Justice Department's repeated legal argument that the House can never sue the executive branch.

House general counsel Douglas Letter noted that discrepancy in a letter last week to the U.S. Court of Appeals for the D.C. Circuit, which is currently weighing a pair of impeachment-related lawsuits. The DOJ responded by saying the two positions do not contradict each other.

Starr said Monday that Trump asserting privileges that prevented the House from hearing certain witness testimony and turning over documents "cannot reasonably be viewed as obstruction, and most emphatically not as an impeachable offense."

The Trump legal defense comes after the House managers spent three days last week laying out their case for the president's removal from office.

Pressure is also building for Senate Republicans to call former national security adviser John Bolton as a witness in the trial, after The New York Times reported that Bolton included conversations in which Trump directly tied withholding Ukrainian military aid to investigations into the Bidens in a book manuscript.

Read more: