FORMER US PRESIDENT Donald Trump joked about his legal challenge while campaigning in Iowa on Tuesday, hours after announcing he had been told he was the target of another investigation.

His appearance at an Elks Lodge in Cedar Rapids came after he posted on his Truth Social platform he had received a letter on Sunday, informing him he was the target of special counsel Jack Smith’s investigation into efforts to overturn the 2020 election, as well as events leading up to the riot at the US Capitol on 6 January 2021.

Any criminal indictment, which often follow such letters, would be Trump’s third since March – he has been indicted in New York and Florida with further potential charges in a separate election interference investigation nearing its conclusion in Georgia.

He told his audience at the Republican county meeting: “I didn’t know practically what a subpoena was and grand juries. Now I’m becoming an expert.”

He incorporated his latest legal woes into his usual stump speech mixture of grievance, lies about the 2020 election, criticism of President Joe Biden and his agenda for a second term.

Taping an interview with Fox News, he told host Sean Hannity he was frustrated by the charges and took the opportunity to attack his opponents.

“It bothers me,” he said. “The DOJ (Department of Justice) has become a weapon for the Democrats.”

Iowa, with its caucuses just six months away, is a critical state for Trump – his party’s decisive early front-runner – and his rivals.

Early polling shows him ahead of his closest rival, Florida Governor Ron DeSantis, by at least 20 to 30 points.

“They are never leaving us because they want to make America great again,” he told local radio before his speech.

“They’re with us. They have a passion like nobody’s ever had.

“The people of our great country, they fully understand what’s going (on). It’s election interference. It’s a weaponisation of justice.”