PALM BEACH, Fla. -- Before most Americans awoke on Saturday, President Trump was on Twitter, posting explosive wiretapping accusations against President Obama. Mr. Trump claims he recently learned Mr. Obama ordered what Mr. Trump describes as a “Watergate-style” wiretap on Trump Tower in New York. He says it happened just before the election.

Mr. Trump offered no evidence and a spokesman for Mr. Obama issued a quick denial. It comes amid growing controversy over the Trump administration’s possible Russian ties, and the president is spending the weekend at his Mar-a-Lago resort in Palm Beach.

Mr. Trump is back on familiar ground here and is back to one of his favorite activities: Stirring up conversation with his tweets. After a week of speeches and appearances widely regarded as “presidential,” Mr. Trump made an explosive allegation that the Obama administration secretly listened in on him during the election.

The president’s tweetstorm started around 6:35 a.m. with this: “Just found out that Obama had my ‘wires tapped’ in Trump Tower. Nothing found.”

Terrible! Just found out that Obama had my "wires tapped" in Trump Tower just before the victory. Nothing found. This is McCarthyism! — Donald J. Trump (@realDonaldTrump) March 4, 2017

Minutes later he asked, “Is it legal for a sitting president to be ‘wire tapping’ a race for president… a new low!”

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! — Donald J. Trump (@realDonaldTrump) March 4, 2017

And, offering no evidence of wiretapping as proof, suggested: “A good lawyer could make a great case” out of the issue.

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! — Donald J. Trump (@realDonaldTrump) March 4, 2017

Ten minutes after that, he compared the allegation to the Nixon-Watergate scandal, saying Mr. Obama is a “bad (or sick) guy.”

How low has President Obama gone to tapp my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy! — Donald J. Trump (@realDonaldTrump) March 4, 2017

A spokesman for Mr. Obama released a statement, saying in part that “neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen. Any suggestion otherwise is simply false.”

President Donald Trump speaking before Congress on Feb. 28, 2017. CBS News

Saturday’s tweets are a departure from the president’s optimistic tone in his widely praised address to a joint session of Congress earlier this week.

“The time for trivial fights is behind us,” Mr. Trump said on Tuesday.

“So I’ll make a comment about the latest tweet -- have you seen it?” Republican Sen. Lindsey Graham said Saturday at a raucous town hall meeting in his home state, South Carolina. The crowd responded “yes!”

At a town hall meeting on March 4, 2017, Sen. Lindsey Graham told the crowd he would investigate President Trump’s claims about wiretapping. CBS News

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

Weekend trips to Florida have become routine for the president -- this is his fourth trip here in six weeks. The White House says this is a “working weekend,” with Mr. Trump focused on revising his controversial travel ban and mapping out a plan to repeal and replace Obamacare.