Chuck Rosenberg, a former FBI chief of staff under former Director James ComeyJames Brien ComeyThe road not taken: Another FBI failure involving the Clintons surfaces Sarah Huckabee Sanders becomes Fox News contributor 3 real problems Republicans need to address to win in 2020 MORE, on Monday said collusion is “absolutely a crime,” a day after President TrumpDonald John TrumpThe Hill's Campaign Report: Democratic field begins to shrink ahead of critical stretch To ward off recession, Trump should keep his mouth and smartphone shut Trump: 'Who is our bigger enemy,' Fed chief or Chinese leader? MORE’s lawyer Rudy Giuliani said it was not a crime.

“Collusion is a crime,” Rosenberg said on MSNBC's "MTP Daily." “We just happen to call it something else, we call it conspiracy, but it is absolutely a crime.”

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“You probably won’t find the crime bank heist in the criminal code but bank robbery is a crime too, and so I am sort of perplexed that it has come down to synonyms,” said Rosenberg, who once headed the Drug Enforcement Administration.

“If these folks don’t know that collusion and conspiracy are synonyms for one another and this is a legal strategy, then they might want to consider changing horses in this race,” Rosenberg added.

In several interviews on Monday, Giuliani asserted that collusion is not a crime.

“I have been sitting here looking in the federal code trying to find collusion as a crime,” Giuliani said on “Fox & Friends.” “Collusion is not a crime.” 

In a later interview on CNN, Giuliani again said that collusion was not a crime.

“I don't even know if that's a crime, colluding about Russians,” Giuliani told CNN. “You start analyzing the crime — the hacking is the crime. The president didn't hack. He didn’t pay them for hacking.”

Trump himself on Tuesday tweeted that collusion was not a crime, adding that it didn't matter any way because there was no collusion between his campaign and Russia, which intelligence agencies have concluded meddled in the 2016 election.

"Collusion is not a crime, but that doesn’t matter because there was No Collusion (except by Crooked Hillary and the Democrats)!" Trump wrote on Twitter.