A U.S. Senator who lost both her legs while serving the Army in Iraq is firing back at "Cadet Bone Spurs."

President Donald Trump complained Monday that Democrats who didn't stand and applaud during his State of the Union address were "un-American" and "treasonous."

"Can we call that treason? Why not?" Trump said in Ohio while promoting the Republicans tax plan. "They certainly didn't seem to love our country very much."

The Hill reports Sen. Tammy Duckworth (D-Ill.) fired back on Twitter Monday, saying she didn't swear an oath "to mindlessly cater to the whims of Cadet Bone Spurs."

Trump attended military high school, but never served in the military due to multiple deferments from the draft during the Vietnam War. One deferment cited heel spurs, or bone protrusions caused by calcium buildup, as a medical explanation for exemption in 1968.

Duckworth is a retired Army lieutenant colonel and Black Hawk pilot who lost her legs when her helicopter was shot down by Iraqi insurgents in 2004. The veteran has clashed with Trump before, criticizing his threats to North Korea and his claims that Democrats were hurting U.S. soldiers by causing a days-long government shutdown.

"I will not be lectured about what our military needs by a five deferment draft-dodger. And I have a message for Cadet Bone Spurs: If you cared about our military, you'd stop baiting Kim Jong Un into a war that could put 85,000 American troops and millions of innocent civilians in danger," Duckworth said on the Senate floor in January.

Sen. Tammy Duckworth, D-Ill., and other senators arrive to vote on the confirmation of Samuel Brownback, governor of Kansas and a former U.S. senator, to become the ambassador-at-large for international religious freedom, at the Capitol in Washington, Wednesday, Jan. 24, 2018.

Duckworth also shared a quote by President Theodore Roosevelt on Monday that telling people not to criticize the President of the United States "is not only unpatriotic and servile, but is morally treasonable to the American public."

Treason, as described in the U.S. Consitition, is a crime against the United States "only in levying war against them, or in adhering to their enemies, giving them aid and comfort. No person shall be convicted of treason unless on the testimony of two witnesses to the same overt act, or on confession in open court."

Trump, who has mocked opponents himself with nicknames like "Lyin' Ted," "Crooked Hillary" and "Cryin' Schumer," has not responded to Duckworth's tweets.

We don't live in a dictatorship or a monarchy. I swore an oath—in the military and in the Senate—to preserve, protect and defend the Constitution of the United States, not to mindlessly cater to the whims of Cadet Bone Spurs and clap when he demands I clap https://t.co/99gW1yalDl — Tammy Duckworth (@SenDuckworth) February 6, 2018