Donald Trump has launched a fresh attack on John McCain, after his widow announced her support for the president's Democratic rival Joe Biden.
Cindy McCain announced her support for Mr Biden in a tweet on Tuesday, saying he was the only candidate "who stands up for our values as a nation."
Mr Trump tweeted that he was "never a fan" of the veteran Republican senator, who died in 2018.
Mr McCain was one of the president's most outspoken Republican critics.
Mr Trump, in turn, publicly questioned his heroism during the Vietnam War.
In her tweet on Tuesday, Mrs McCain said while her husband and Mr Biden had some "passionate arguments" and while she did not "always agree on the issues" with the Democratic presidential candidate, "he is a good and honest man".
In response, President Trump said she "can have Sleepy Joe!" - a nickname the president has for his rival.
"I hardly know Cindy McCain," he added, "other than having put her on a Committee at her husband's request."
Cindy McCain made an address at the Democratic National Convention last month, and her endorsement may prove a hindrance to President Trump, who is trailing Mr Biden in most national polls.
Mr Biden has since thanked her, saying on Twitter that he was "deeply honoured" to have her support and friendship.
Mr McCain was the Republican party's presidential candidate in 2008, and a senator for Arizona, a key battleground state in November's elections.
President Trump is in hospital after being diagnosed with Covid-19
He has taken an experimental drug and antiviral medication and his doctor said he was "doing very well"
First Lady Melania Trump also has the virus and is recuperating at the White House
Ex-adviser Kellyanne Conway, campaign manager Bill Stepien and two Republican senators - Mike Lee and Thom Tillis - all test positive
But Joe Biden, who took part in the first US presidential debate with Trump on Tuesday, has tested negative
Trump, 74, has been criticised for playing down severity of virus and often spurning masks and social distancing
There have been more than 7m infections with Covid in the US, and more than 200,000 deaths
