Trump has repeatedly said that putting conservatives on the court - Kavanaugh is his second appointment - was among the top goals of his presidency.
Kavanaugh was "caught up in a hoax set up by the Democrats", Trump told reporters, without elaborating.
As Kavanaugh won't vote in any cases prior to his tenure, these votes could end in a 4-4 tie, leading to either a reinstatement of the lower court ruling or a retrial with Kavanaugh.
"I want to apologize to Brett and the entire Kavanaugh family for the awful pain and suffering you have been forced to endure", Trump said at the evening White House 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.
Although Kavanaugh was formally sworn in as a Supreme Court justice on Saturday evening after the final voting - while angry protesters banged on the huge front doors of the court building in Washington - there was due to be a ceremonial swearing-in at the White House on Monday evening where Trump himself will administer the oath of office.
He called the Kavanaugh row "a disgraceful situation brought about by people who are evil", and said that the result was "very exciting".More news: Betting suspended on The Everest
Hours before Monday evening's White House event, Trump accused opposition Democrats of already plotting to remove Kavanaugh from the bench.
Kavanaugh also announced that all four of his law clerks will be women - "a first in the history of the Supreme Court". An FBI report into sexual misconduct allegations made against Kavanaugh, has not been released to the public.
Those who were there held signs saying, "We will not forget" and "We do not consent", following the acrimonious fight that culminated in Kavanaugh's 50-48 Senate confirmation Saturday.
"The reality is, right now, Republicans control the House and the Senate, and there's no way to do even an investigation unless we flip one of the houses", replied Booker, a Democrat seen as a potential presidential candidate in 2020.
The justices on Tuesday left in place an August 2017 ruling the new Supreme Court justice wrote that struck down an Obama-era Environmental Protection Agency rule.
"The Supreme Court is an institution of law".
Kavanaugh will hear his first Supreme Court case, a day after President Trump swore in his nominee.
Many observers have noted that Kavanaugh's confirmation itself represent a triumph of minority rule, in two senses. The president's rendering of a verdict on the sexual assault allegations risks further antagonising political opponents at a moment that the "Me Too" movement demands accountability for sexual misconduct.