President Donald Trump "acted alone" when he sent racist tweets suggesting four Democratic representatives should "go back" to their "broken and crime-infested countries," according to the Washington Post.

The Post cited 26 lawmakers and White House insiders, detailing how Trump's inner circle, including senior adviser Kellyanne Conway and Republican Sen. Lindsey Graham, felt he had crossed a line.

The tweets set off a week of public swipes over the tweets, as Democrats offered public condemnation and Trump supporters seized on the racist rhetoric.

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President Donald Trump acted alone and impulsively in issuing racist tweets about four progressive freshman congresswomen, according to The Washington Post.

The report says members of the president's inner circle, including senior adviser Kellyanne Conway and Republican Sen. Lindsey Graham, felt he had crossed a line with the tweets that set off fury from both Republican allies and his political opponents.

The Post cited "26 White House aides, advisers, lawmakers and others involved in the response" who described the White House and Republicans as taken by surprise by the tweets.

Trump tweeted on July 14 that Democratic representatives Alexandria Ocasio-Cortez, Rashida Tlaib, Ayanna Pressley, and Ilhan Omar should "go back" to their "broken and crime-infested countries," though three out of four of them were born in the US, and all four are US citizens and elected representatives.

Read more: Timeline of the chaotic series of events surrounding Trump's racist tweets attacking 'the Squad'

Republicans largely ignored the tweets before offering soft condemnation as the White House and Trump's campaign sought damage control to insulate "key supporters," according to the Post. Democrats, including lawmakers and 2020 contenders, hit back with a relatively united front offering flat condemnation of the racist rhetoric.

Trump rejected the blowback against the tweets two days later, saying he doesn't have a "racist bone" in his body. Ocasio-Cortez hit back in a tweet that said, "You're right, Mr. President — you don't have a racist bone in your body. You have a racist mind in your head, and a racist heart in your chest."

The tweets resurfaced at a North Carolina Trump rally later in the week when supporters chanted "Send her back."

Trump initially disavowed the chants, stating he wasn't "happy" about them and falsely claimed he attempted to stop the chants, despite video evidence showing that isn't the case. The next day, Trump reversed his position, saying they are "incredible people... those are incredible patriots."