A day after his third indictment, a defiant Donald Trump on Wednesday said he has "never had so much support" as he gears up for the next year's race for the White House.

The 45-page indictment alleges that the former US president, a Republican, plotted a conspiracy aimed to keep him in power after he was defeated by Joe Biden, a Democract, in the 2020 general election.

It accused Trump, 77, of knowingly spreading "pervasive and destablising lies" about election fraud that threatened the presidential election and therefore American democracy.

But in an all-caps post on his Truth Social platform, Trump wrote that he has "never had so much support" as he does after the latest federal charges against him.

Referring to the indictment as "unprecedented", Trump says it "has awoken the world to the corruption, scandal, & failure that has taken place in the United States for the past three years".

Thanking his supporters for rallying to his defence, Trump described his indictment as "unprecedented" and vowed to make America great again.

"America is a nation in decline, but we will make it great again, greater than ever before. I love you all!!!" He is expected to appear before a judge on Thursday in his first court appearance in the case.

Trump’s attorney slammed special counsel Jack Smith for indicting his client in the January 6 probe, saying it’s a "terribly tragic day." John Lauro said the 45-page indictment shows that political speech has been "criminalised." "Joe Biden's running against Donald Trump and losing currently. And now we have [the] Justice Department indicting President Trump for actions that he took as the executive, as the chief executive of the United States with respect to public policy matters," he told Fox News.

"So now we have the criminalisation and the weaponisation of public policy and political speech by one political party over another," he was quoted as saying.

In his social media post, Trump also claimed that latest polls show he is leading much ahead of his rivals in national opinion polls for both the Republican Party's nomination and the general election in 2024.

Polls do show him well ahead of his Republican rivals, but most polls show him neck-and-neck with President Biden, who is seeking re-election next year.

Trump has now been charged in three criminal cases. The other cases relate to the classified documents Trump kept at his Mar-a-Lago residence in Florida after he left the White House and hush payments to Stormy Daniels, a former porn star.

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