The Kentucky Republican said on Thursday at the Senate floor that the Democratic-controlled House's decision impeach Trump was rushed, reports Efe news.
"More than a year of hearings for (Richard) Nixon, multiple years of investigation for (Bill) Clinton - and they've impeached President Trump in 12 weeks. Twelve weeks," McConnell said.
On Wednesday night, the Democratic-controlled House of Representatives voted along party lines to impeach Trump on two articles of impeachment.
House Democrats approved articles accusing the President of abuse of power and obstruction of Congress.
"This particular House of Representatives has let its partisan rage at this particular president create a toxic new precedent that will echo well into the future," McConnell said.
"If the Senate blesses this slapdash impeachment, if we say from now on this is enough, then we invite an endless parade of impeachment trials."
House Speaker Nancy Pelosi said after the vote that the articles of impeachment would not be submitted immediately to the Republican-controlled Senate.
McConnell ripped Pelosi for not sending the articles to the Upper House of Congress.
"Looks like the prosecutors are getting cold feet," the Senate Majority leader said.
Pelosi, for her part, said on Thursday that she was not trying to delay the start of Trump's trial in the Senate and was waiting for the House managers, or prosecutors, to be chosen before delivering the articles to the upper house.
She defended her decision to move forward with the impeachment.
"It reminded me that our founders, when they wrote the Constitution, they suspected there could be a rogue president. I don't think they suspected we could have a rogue President and a rogue leader in the Senate at the same time," Pelosi said.
House Democrats launched the impeachment inquiry based on an allegation that Trump sought personal political gain this year by improperly pressuring Ukrainian President Volodymyr Zelensky to publicly announce a corruption investigation into former US Vice President Joe Biden, a leading contender for the 2020 Democratic presidential nomination, and his son, Hunter.
Democrats also alleged that Trump obstructed the House impeachment inquiry by blocking officials from testifying and preventing the sharing of federal government documents with Congress.
A trial, probably starting in January, will be held in the Republican-controlled Senate, where a highly unlikely two-thirds super-majority (67 out of 100 senators) would be needed to convict Trump and remove him from office.
Trump is only the third US president to be impeached.
Andrew Johnson (in the 19th century) and Bill Clinton - 21 years ago - were both impeached by the House and acquitted by the Senate, while Richard Nixon resigned in 1974 before the lower house could vote on his impeachment.
( With inputs from IANS )