Tulsi Gabbard, a former Democratic congresswoman, has endorsed the Republican nominee, Donald Trump, in the US presidential election.

Gabbard, who served in the military in Iraq, ran for president in the Democratic primary in 2020. She quit the party two years later and has become a fixture at conservative conferences and in rightwing media.

Addressing a National Guard Association conference in Detroit, Michigan, where Trump was speaking, Gabbard said: “This administration has us facing multiple wars on multiple fronts in regions around the world and closer to the brink of nuclear war than we ever have been before.

“This is one of the main reasons why I’m committed to doing all that I can to send President Trump back to the White House, where he can once again serve us as our commander-in-chief. Because I am confident that his first task will be to do the work to walk us back from the brink of war.”

Gabbard, who represented Hawaii in Congress and is a former vice-chair of the Democratic National Committee, accused the Democratic nominee, Kamala Harris, of retaliating against political opponents, undermining civil liberties and weaponising America’s institutions against both Trump and herself.

“We as Americans must stand together to reject this anti-freedom culture of political retaliation and abuse of power,” she added.

Gabbard’s announcement comes a day after Robert F Kennedy Jr, scion of a Democratic dynasty, suspended his own White House bid and threw his weight behind Trump. Elon Musk, who describes himself as “historically a moderate Democrat”, is also backing the former president.

Trump, who has been portraying Harris as a leftwing extremist, told the gathering on Monday: “This fight is no longer between Democrats and Republicans. This is a fight between communism and freedom.

“It’s a very serious fight. That’s why millions of traditional Democrats, including FDR Democrats, JFK Democrats, independents and old-fashioned liberals are joining our movement. Our poll numbers are great.”

Trump admitted that he had not been aware that Gabbard served as a lieutenant-colonel in the army. “She’s a special person,” he added. “She’s got great common sense, great spirit. She loves our country and she loves the people in this room.”

Recently Gabbard has been helping Trump prepare for next month’s televised presidential debate against Harris. In 2020 she took Harris to task on the debate stage over her record as a prosecutor – a clip that still circulates in rightwing media.

Trump, who earlier laid wreaths during a ceremony at Arlington National Cemetery, was marking the third anniversary of a suicide bombing that killed 13 US service members during the withdrawal from Afghanistan. “The humiliation in Afghanistan set off the collapse of American credibility and respect all around the world,” he said in Detroit, seeking to blame Harris and Joe Biden for the deaths.

In her own statement marking the anniversary of the Kabul airport attack, Harris said she mourns the 13 service members who were killed. “My prayers are with their families and loved ones,” she added. “My heart breaks for their pain and their loss.”