President Trump's decision to order the airstrike that killed top Iranian Gen. Qassem Soleimani was ill-advised and is likely to make the region far more dangerous for American troops, 2020 Democratic presidential candidate Pete Buttigieg said Monday.

"There is no question that Soleimani had American blood on his hands and that he was a bad actor in the region. But if there is anything that we have learned in the last 20 years about the Middle East, it's that taking out a bad guy is not necessarily a good idea," the South Bend, Indiana mayor said on "Morning Joe."

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Buttigieg said the administration has shown no evidence that they have "really thought about the consequences" of the strike. The former Naval intelligence officer, who served in Afghanistan in 2014, expressed concern for the American soldiers who are now on their way to the region amid rising tensions.

"Having known what it's like to be on the inside of one of those airplanes, you need to be able to trust that everybody up your chain of command has thought through what's ahead, and we're just not seeing a lot of indications of that," he said, warning that Iran appears poised to move ahead with its nuclear program and the Iraqi government may now try to expel U.S. troops.

"So, if they were thinking about this in terms of the 3D chess it is and not checkers, we've not seen evidence of why they felt this was the only or best decision."

Earlier Monday, the daughter of slain Iranian Gen. Qassem Soleimani warned the families of U.S. soldiers deployed in the Middle East that they "will spend their days waiting for the death of their children" during the funeral Monday in Tehran.

While speaking to a vast crowd at Enqelab-e-Eslami (Islamic Revolution) square, Soleimani's daughter, Zeinab, directly threatened an attack on the U.S. military in the region, following an increase in tensions between Tehran and Washington.

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"Families of the American soldiers in western Asia have witnessed America's humiliation in Syria, Iraq, Lebanon, Afghanistan, Yemen and Palestine wars, and will spend their days waiting for the death of their children," she said in Farsi, which was translated by the Associated Press.

During the funeral, Iran's Supreme Leader Ayatollah Ali Khamenei -- who had a close relationship with Soleimani -- wept and prayed over his casket during the traditional Muslim prayers for the dead. The ceremony came on the heels of Trump issuing a tweet that he said would "serve as notification" to Congress about military action against Iran.

“These Media Posts will serve as notification to the United States Congress that should Iran strike any U.S. person or target, the United States will quickly & fully strike back, & perhaps in a disproportionate manner,” he tweeted Sunday afternoon.

“Such legal notice is not required, but is given nevertheless!”

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Buttigieg said Trump is not handling the situation properly with respect to informing Congress, arguing that the Senate's Gang of Eight -- a group of top Republican and Democratic lawmakers -- should have been notified.

"That heads-up to Congress is to Congress as a body, not to certain members who agree with you politically ... You don't notify Congress by tweet," he responded.

Fox News' David Aaro and Associated Press contributed to the report