President Donald Trump launched a Twitter attack against his former chief of staff on Thursday after John Kelly defended a national security official who testified against Trump during the House impeachment inquiry.

"When I terminated John Kelly, which I couldn't do fast enough, he knew full well that he was way over his head. Being Chief of Staff just wasn't for him. He came in with a bang, went out with a whimper, but like so many X's, he misses the action & just can't keep his mouth shut," Trump tweeted, according to The Independent.

Trump also said Kelly has a "military and legal obligation" to keep quiet about the time he spent in the Trump administration and his thoughts about the president. But The Independent noted that “Kelly has never mentioned signing a non-disclosure pact and was not an active-duty Marine when he worked in the administration.”

Unsatisfied by lashing out at Kelly alone, Trump also brought the former chief of staff’s wife into the mix, tweeting: "His incredible wife, Karen, who I have a lot of respect for, once pulled me aside & said strongly that 'John respects you greatly. When we are no longer here, he will only speak well of you.' Wrong!"

Kelly found himself the subject of Trump’s ire after he “offered his most blunt and candid comments since being ousted about his former boss” on Wednesday night during an event at a college in New Jersey.

At one point during the event, Kelly defended Lt. Col. Alexander Vindman, who testified during the impeachment inquiry that he believed Trump’s attempt to score political dirt on Joe Biden from Ukraine was inappropriate.

"We teach them, 'Don't follow an illegal order. And if you're ever given one, you'll raise it to whoever gives it to you that this is an illegal order, and then tell your boss,” Kelly said. “He did exactly what we teach them to do from cradle to grave. He went and told his boss what he just heard.”

Kelly also gave his thoughts on Trump’s attempt to work out a deal with North Korea, saying, "[Kim Jong Un] will never give his nuclear weapons up. Again, President Trump tried -- that's one way to put it. But it didn't work.” He added that he “never did think Kim would do anything other than play us for a while, and he did that fairly effectively."

White House press secretary Stephanie Grisham joined Trump’s attack on Fox News Thursday morning, saying, "I worked with John Kelly, and he was totally unequipped to handle the genius of our great President.”

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