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WASHINGTON — Alan Dershowitz, the retired Harvard law professor who is serving on the impeachment defense team, argued Monday night that even if explosive allegations made by former national security adviser John Bolton in a an upcoming book are true, they don't rise to the level of impeachment.

The New York Times reported Sunday night that in the book's unpublished manuscript, Bolton says President Donald told him that nearly $400 million in aid to Ukraine wouldn't be released until it offered assistance into investigations of Democratic targets, including former Vice President Joe Biden and his son Hunter Biden.

"If a president, any president, were to have done what The Times reported about the content of the Bolton manuscript, that would not constitute an impeachable offense. Let me repeat: Nothing in the Bolton revelations, even if true, would rise to the level of an abuse of power or an impeachable offense," Dershowitz said on the Senate floor.

NBC News hasn't seen a copy of the manuscript or verified the report, which cited multiple sources familiar with Bolton's account.

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Dershowitz said the Constitution makes it clear that "you cannot turn conduct that is not impeachable into impeachable conduct simply by using words like 'quid pro quo' and 'personal benefit.'" He added that the framers wouldn't have "promiscuously" used a term like "abuse of power to be weaponized as a tool of impeachment."

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"It is precisely the kind of vague, open-ended and subjective term that the framers feared and rejected," he said.

Dershowitz was the first member of Trump's legal team Monday to raise the Bolton report, which has added more weight to Democrats' demands to hear from witnesses.

Sunday's report prompted two Republican senators — Mitt Romney of Utah and Susan Collins of Maine — to argue Monday that the developments give greater weight to the need to call witnesses. Romney said it's "increasingly likely" that enough Republican senators will vote to call witnesses. Bolton has said he is willing to testify if subpoenaed.

Trump denied having made the comments to Bolton.

"I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens. In fact, he never complained about this at the time of his very public termination. If John Bolton said this, it was only to sell a book," Trump said.

Dershowitz also said Monday that if, hypothetically, a Democratic president told Israel that foreign aid authorized by Congress wouldn't be sent or that an Oval Office meeting wouldn't be scheduled unless the Israelis stopped building settlements, it would be a quid pro quo but not an abuse of power.

"I might disapprove of such a quid pro quo demand on policy grounds, but it would not constitute an abuse of power. Quid pro quo alone is not a basis for abuse of power. It's part of the way foreign policy has been operated by presidents since the beginning of time," he said.

That scenario, however, is much different from what Trump was impeached for. Democratic House managers have argued that Trump demanded that Ukraine investigate Joe Biden, a potential 2020 rival, and his son in exchange for the release of U.S. aid to Ukraine and a White House meeting. Democrats said he did it for his own personal gain, to "cheat" in the election.

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Sen. Elizabeth Warren of Massachusetts, a Democratic presidential candidate who is a former Harvard colleague of Dershowitz's, said in a tweet that his "argument is contrary to both law & fact."