The ex-president devoted a large portion of his address at the Conservative Political Action Conference to the "sick and corrupt" electoral process, pointing to the high court’s refusal to hear GOP challenges to state courts that changed voting rules before the election.
"This election was rigged and the Supreme Court and other courts didn’t want to do anything about it," Mr Trump said.
"They didn’t have the courage, the Supreme Court, they didn’t have the courage to act, but instead used process and lack of standing."
The Supreme Court voted 6-3 last week not to hear a case that claimed Pennsylvania's state government and courts circumvented the state legislature when it changed rules for mail-in ballots and voting deadlines.
The court refused to hear the case since the election was over. In his dissent, Justice Clarence Thomas said the decision leaves election law hidden beneath a shroud of doubt.
Mr Trump said the court, one-third of which he appointed, should be "ashamed of themselves" for what they did to the country.
"They didn’t have the guts or the courage to make the right decision. They didn’t want to talk about it," Trump said.
Mr Trump also referenced the case brought by Texas attorney general Ken Paxton, which was also dismissed by the court.
"Our election process is worse than that in many cases of a third world country. You know that, you saw what was going on. Even if you consider nothing else, it is undeniable that election rules were illegally changed at the last minute in almost every swing state with the procedures rewritten by local politicians," Mr Trump said.
He added: "Regardless of your political views, this should concern you as a constitutional matter. And the Supreme Court, again, didn’t have the guts or the courage to do anything about it. And neither did other judges. And Democrats even admitted in Time magazine."
The allegation was in reference to a Time article titled “The Secret History of the Shadow Campaign That Saved the 2020 Election”, which says a "cabal of powerful people" worked behind the scenes to "influence perceptions, change rules and laws, steer media coverage and control the flow of information".
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