Donald Trump's claim that Hillary Clinton was part of the founding of the Islamic State is "disrespectful to the military that is out there fighting ISIS every day," one of the first members of Congress to endorse Clinton said Sunday

Sen. Claire McCaskill, D-Mo., said in an interview on "Fox News Sunday" that there are a lot of reasons for the rise of ISIS, including a Status of Forces Agreement negotiated by President George W. Bush.

"We couldn't leave our troops in Iraq, even if the president wanted to because the parliament in Iraq was refusing to give them immunity," McCaskill explained.

In regards to the SOFA, Trump probably thinks it is "a gilded couch at Mar-a-Lago, he probably doesn't even know what SOFA is, but that was a very relevant part of the this," McCaskill remarked.

Critics say Obama failed to negotiate aggressively enough to renew the Status of Forces agreement and note he also campaigned on what he characterized as his success in withdrawing combat troops from Iraq.

"It was also important to realize that Assad, by what he did in his country, allowed ISIS to move into ... Syria and get strongholds and recruit," McCaskill added. "That was the work and support of [Russian President Vladmir] Putin who is Trump's best buddy, so you can say Trump and his friend Putin are the founder of ISIS, which probably would be more accurate than calling out the commander in chief in that way."

Last week, Trump, the Republican presidential nominee, linked President Obama and Clinton to the founding of ISIS.

"ISIS is honoring President Obama," Trump said Wednesday during a rally in Fort Lauderdale, Fla. "He's the founder of ISIS. He founded ISIS. I would say the co-founder would be Crooked Hillary Clinton."

Trump has since defended his comments as "sarcastic."

McCaskill endorsed Clinton for president in June 2013, despite backing President Obama over the former secretary of state in the 2008 cycle.