President Trump, in a Saturday morning tweetstorm, responded to the mounting questions over his ties to Russia by accusing then-President Obama of wiretapping him at Trump Tower just before the November election — an accusation an Obama spokesman rejected as "simply false."

The unsubstantiated outburst follows several days of stories raising questions about meetings between members of the Trump campaign and Russian officials, particularly two previously undisclosed meetings between now Attorney General Jeff Sessions and Russian ambassador Sergei Kislyak.

"How low has President Obama gone to tapp [sic] my phones during the very sacred election process," he writes. "This is Nixon/Watergate. Bad (or sick) guy!"

Kevin Lewis, Obama's spokesman, said in a statement: "A cardinal rule of the Obama Administration was that no White House official ever interfered with any independent investigation led by the Department of Justice.

"As part of that practice, neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen," he said. "Any suggestion otherwise is simply false."

In making the charges, Trump did not elaborate on any evidence backing up the explosive accusation.

American law enforcement and intelligence agencies were known to have been examining intercepted communications and financial transactions as part of a broad investigation into possible links between Russian officials and Trump associates, The New York Times reported in January.

The investigation was being led by the FBI, aided by the National Security Agency, the CIA and the Treasury Department’s financial crimes unit, the Times said.

Electronic surveillance under such an investigation would require a warrant approved by a FISA court judge. Presidents do not have the authority to order such wiretaps and would not as a routine matter even be aware of them.

If Trump were privy to information that his phone was indeed wire tapped, it would suggest that a FISA court had found probable cause to issue such a warrant.

Sen. Chris Coons, D-Del., told MSBNC this week that he believes the FBI is in possession of transcripts which might detail communication between top Trump campaign members and Russian officials. The transcripts, which Coons said he has not seen, could reveal if the Kremlin and Trump’s team colluded to influence the 2016 election.

Ben Rhodes, Obama's foreign policy adviser, responded to Trump in a series of tweets, first stating that "No President can order a wiretap. Those restrictions were put in place to protect citizens from people like you."

Sen. Lindsey Graham, R-S.C., said during a Clemson town hall meeting this morning that it would be the biggest political scandal since Watergate if it’s true that Obama either wiretapped Trump’s phones, illegally — or was able to obtain a warrant to lawfully monitor Trump’s campaign activity with foreign governments. Either scenario is worrisome, he said.

“It’s my job as a United States senator to get to the bottom of this,” he said to applause. “I promise you I will.”

The tweet blasts began at 6:26 a.m. from the Winter White House at Mar-a-Lago in Florida when Trump raised the Sessions issue by noting the first meeting between the senator from Alabama and the Russian ambassador was set up by the Obama administration as part of an education program.

Eight minutes later, he raised the charge of illegal surveillance by the Obama administration: "Terrible! Just found out that Obama had my "wires tapped" in Trump Tower just before the victory. Nothing found. This is McCarthyism!"

Then: "Is it legal for a sitting President to be "wire tapping" a race for president prior to an election? Turned down by court earlier. A NEW LOW!"

And: "I'd bet 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!"

To that, Rhodes responded: "No. They couldn't. Only a liar could do that."