The former Republican leader called the raid “one of the most shocking abuses of power by any administration in American history” and “a travesty of justice”.
“They’re trying to silence me and more importantly they’re trying to silence you – but we will not be silenced, right?” Mr Trump said in Wilkes-Barre, Pennsylvania on Saturday night.
Investigators recovered thousands of documents in the search of his Florida property, including more than 100 with classified and top secret markings.
Mr Trump’s endorsed picks won many Republican primaries this summer, but many of the candidates he backed were inexperienced and polarising figures now struggling in their November races.
That is putting Senate control — once assumed to be a lock for Republicans — on the line.
Mr Trumps picks include Dr Mehmet Oz, a television personality and Republican Pennsylvania candidate, author JD Vance in Ohio, venture capitalist Blake Masters in Arizona and former football star Herschel Walker in Georgia.
“Republicans have now nominated a number of candidates who’ve never run for office before for very high-profile Senate races,” said veteran Republican pollster Whit Ayres.
While he is not writing his party’s chances off just yet, he said: “It’s a much more difficult endeavour than a candidate who had won several difficult political races before.”
The stakes are particularly high for Mr Trump as he lays the groundwork for an expected 2024 presidential run amid a series of escalating legal challenges.
This past week, President Joe Biden gave a prime-time speech in Philadelphia warning Mr Trump and other “Maga” Republicans — the acronym for “Make America Great Again” — posed a threat to US democracy.
Mr Trump repeatedly attacked Mr Biden, saying at one point “above all this election is a referendum on the corruption and extremism” of Mr Biden and Democrats — and gave a brief spotlight to Mr Oz and Doug Mastriano, the GOP nominee for governor of Pennsylvania.
Mr Mastriano, he noted, had fought with him from the beginning to try to help Mr Trump overturn the 2020 election and stay in power, saying he fought “like very few people fought”.
While Republicans were once seen as having a good chance of gaining control of both chambers of congress in November, benefitting from soaring inflation, high gas prices and Mr Biden’s slumping approval ratings, they have found themselves on the defensive since the US Supreme Court overturned the landmark Roe versus Wade decision protecting abortion rights.
Some candidates, like Mr Mastriano, are sticking with their primary campaign playbooks, hoping they can win by turning out Mr Trump’s loyal base even if they alienate or ignore more moderate voters.
But others have been trying to broaden their appeal, scrubbing from their websites references to anti-abortion messaging that is out of step with the political mainstream.
Others have played down Mr Trump endorsements that were once featured prominently.