Duckworth portrayed Trump as a puppet of Russian President Vladimir Putin.

Standing next to her wheelchair with her prosthetic legs showing, Duckworth criticised Trump for refusing to confront Putin over Russia's reported payment of bounties to Afghan forces for the killing of American troops.

With the US Capitol as her backdrop, the Illinois senator contrasted Trump with his Democratic challenger, Joe Biden, saying the former vice president understands military sacrifice from his late son Beau Biden's deployment to Iraq in the Delaware National Guard.

"That's the kind of leader our service members deserve, one who understands the risks they face, and who would actually protect them by doing his job as commander in chief," Duckworth said.

"Instead, they have a coward in chief who won't stand up to Vladimir Putin, read his daily intelligence briefings, or even publicly admonish adversaries for reportedly putting bounties on our troops' heads."

Duckworth, a former US Army helicopter pilot who was awarded the Purple Heart, was one of the top contenders to be Biden's running mate before he chose California Senator Kamala Harris.

"As president Joe Biden would never let tyrants manipulate him like a puppet," she said.

"He would never pervert our military to stroke his own ego. He would never turn his back on our troops or threaten them against Americans peacefully exercising their constitutional rights.

"Joe Biden would stand up for what's right. Stand tall for our troops and stand strong against our enemies, because, unlike Trump, Joe Biden has common decency."

Duckworth, 52, served four years in the House before winning her Senate seat four years ago. She was assistant secretary of Veterans Affairs under President Barack Obama and, before that, director of the Illinois Department of Veterans Affairs.

Australian Associated Press