Kavanaugh, in turn, attacked the Dem senators on the Senate Judiciary Committee for what he called an orchestrated "hit" meant to exact revenge for the Clintons, warning the Dems on the committee "what goes around comes around".
The president - whose Republicans fear losing at least the lower house of Congress in November - angrily predicted that the Kavanaugh row would backfire on Democrats. Only one Democrat voted for Trump's nominee.
"On behalf of our nation, I would like to apologize to Brett and his family for the bad pain and suffering that you have been forced to endure", Trump, standing in the East Room of the White House, said in the televised event.
The official swearing-in had take place on Saturday, but Trump chose to replicate the event this evening in the East Room of the White House.
During this historic Supreme Court justice swearing in-cum-Dem-smackdown, Trump said "In our country a man or a woman must always be presumed innocent unless and until proven guilty" adding, "And with that, I must state that you sir, under historic, scrutiny were proven innocent".
Monday's ceremonial swearing-in ceremony at the White House wrapped up a dramatic confirmation process that lasted one day shy of three months - and put the #MeToo movement front and center after professor Christine Blasey Ford came forward and testified, alleging Kavanaugh had attempted to rape her when the two were Maryland teens. Kavanaugh replaced Kennedy on the bench.
Kavanaugh said at the swearing-in ceremony on Monday that "the Senate confirmation process was contentious and emotional".
"I think a lot of Democrats are going to vote Republican", he said in his earlier comments outside the White House.
When Trump purports to apologize to Kavanaugh on behalf of the "nation" while sneeringly dismissing those claims, even as a majority opposes Kavanaugh and believes those charges, Trump is - unwittingly or not - highlighting the degree to which this episode represents the further entrenchment of minority rule.
Only one US supreme court justice has ever been impeached - Samuel Chase, in 1804, who was acquitted by the Senate.
Kavanaugh is expected to begin his tenure by hearing two cases dealing with matters of robbery and burglary.
Samuel Chase in 1804 was the only justice to be impeached by the House.
The Supreme Court will be hearing a case about an immigrant who has a prior criminal record but is now out of prison.
Independent court analysts, however, predict Kavanaugh is likely to concur with more conservative interpretations of the law, given a solid 5-4 ideological edge on the court to those who lean to the right.