WASHINGTON (AFP, REUTERS) - US President Donald Trump on Wednesday (Sept 23) launched a fresh mocking attack on Mr John McCain, the Republican senator who died in 2018, after Mr McCain's widow threw her support behind Mr Joe Biden in the election.

In a particularly aggressive tweet, the Republican leader once again criticised Mr McCain, who was one of the few in the Republican party to openly castigate him.

"I hardly know Cindy McCain other than having put her on a Committee at her husband's request," he tweeted.

"Joe Biden was John McCain's lapdog," he said of the Democratic challenger he will face as he seeks a second four-year term on Nov 3.

Denouncing "bad decisions on endless wars", Mr Trump stated that he was "never a fan of John".

"Cindy can have Sleepy Joe!" concluded the President.

Mrs Cindy McCain's support for Mr Biden, announced on Tuesday, is a setback for Mr Trump, who faces an uphill challenge in the election and boasts of having the entire Republican party behind him.

The widow of the former senator tweeted: "We are Republicans, yes, but Americans foremost. There's only one candidate in this race who stands up for our values as a nation, and that is @JoeBiden."

Mr Biden, who forged a long friendship with Mr McCain despite their ideological differences, had broken the news earlier during a virtual fund-raiser, telling supporters that Mrs McCain decided to endorse him after The Atlantic magazine reported that Mr Trump had called US soldiers who died in combat "losers" and "suckers".

Mr Trump has denied making the comments.

The President and Mr McCain had a history of animosity, after Mr Trump disparaged Mr McCain's military service and years spent as a prisoner of war in Vietnam during the 2016 presidential campaign.