(CNN) President Donald Trump did not need advisers to talk him into approving the US strike that killed Iranian military commander Qasem Soleimani, according to a Republican congressional source familiar with the administration's decision to take out the general.

While in the past, the source acknowledged that the President "has been reluctant to take military action," in this case, the killing of an American contractor , the wounding of others, and the subsequent protests at the US embassy in Baghdad "crossed his line." His advisers also pointed out to the President that if he "didn't respond now, they (Iran) will continue to cross it."

"I am very confident he was not reluctant," said the source. When Trump finally gets ready to act, the source added, "you can't out-escalate him."

Trump drew a significant red line in a three-part tweet on Saturday, vowing specific military action against Iran if it "strikes any Americans, or American assets."

"We have ... targeted 52 Iranian sites (representing the 52 American hostages taken by Iran many years ago), some at a very high level & important to Iran & the Iranian culture" and "if Iran strikes any Americans, or American assets... Iran itself, WILL BE HIT VERY FAST AND VERY HARD," Trump wrote in a series of tweets.

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