There might be truth to allegations made by President Donald Trump that Trump Tower was wiretapped during last year's presidential election, former U.S. Attorney General Michael Mukasey said Sunday.

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"This is the difference between being correct and being right," Mukasey, who served as attorney general under President George W. Bush, said during an appearance on ABC's "This Week."

"I think the president was not correct, certainly, in saying that President (Barack) Obama ordered a tap on a server in Trump Tower," he said. "However, I think he's right in that there was surveillance and that it was conducted at the behest of the attorney – of the Justice Department."

Trump took to Twitter over the weekend with allegations against the former president, writing on Saturday that "a good lawyer could make a great case out of the fact that President Obama was tapping my phones in October, just prior to election!"

However, Mukasey said, if the allegation about wiretapping proves true, it would have been part of an intelligence-gathering investigation and approved by the Foreign Intelligence Surveillance Act court. The court handles requests by intelligence agencies for surveillance warrants aimed at foreign spies operating in the U.S.

"It means there were some basis to believe that somebody in Trump Tower may have been acting as an agent of the Russians, for whatever purpose, not necessarily the election, but for some purpose," Mukasey said.

Obama has denied ordering a wiretap on Trump Tower.

"Neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen," Obama spokesman Kevin Lewis said in a statement over the weekend. "Any suggestion otherwise is simply false."

Trump has not provided evidence to support his claim. He has called for Congress to investigate whether Obama abused his power while in office.