President Trump accused his predecessor, Barack Obama, of wiretapping Trump Tower during the campaign in October, in a series of tweets Saturday morning

"Terrible! Just found out that Obama had my "wires tapped" in Trump Tower just before the victory. Nothing found. This is McCarthyism!", Trump first tweeted. Then the president sent out a tweet about the 22 times the Russian ambassador reportedly visited the White House, including four times last year.

Obama, the 44th president, left the White House in January. He had supported and campaigned for Democratic candidate Hillary Clinton during the 2016 presidential campaign.

Trump's next tweet compared the wiretap to the Watergate scandal that led to the resignation of President Richard Nixon.

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

The president then mentioned he might look into a "good lawyer" to make a "great case" out of the wiretap.

"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!", Trump tweeted.

He added: "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!"

The president has not provided any evidence of wiretapping. Trump has tweeted out unfounded claims in the past.

Trump is possibly reacting to a Breitbart story published Friday, which explores conservative radio host Mark Levin's claim a day prior on "police tactics" the Obama administration used to undermine Trump's campaign. The article discusses reports about the Obama administration applying for a FISA court warrant to tap Trump Tower in New York City to investigate suspected links to Russian banks.

Trump's chief strategist, Steve Bannon, was previously Breitbart News' chief executive.

A spokesperson for former President Barack Obama says President Trump's assertion that Obama unlawfully wiretapped Trump Tower during the 2016 presidential campaign is "simply false."

"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," said Obama spokesman Kevin Lewis in a statement Saturday afternoon. "As part of that practice, neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen. Any suggestion otherwise is simply false."

A federal judge would need to find probable cause in order to approve any such surveillance activities. Sen. Ben Cardin, D-Md., ranking member of the Foreign Relations Committee, suggested there be a independent investigation on CNN on Saturday.

"There are certainly legal protections in all these areas," Cardin said. "Rather than getting the president's interpretation of what he thinks happened, why not an independent investigation? I'm for including all this. Let the independent commission look at the entire aspect of what Russia is doing here in the United States including how we responded. ... "If there is anything like what he's tweeting about, it would be under supervision of the courts."

There has been some pushback against Trump's claims from former Obama administration officials.

CNN and NBC reported unnamed officials denying Trump's claims on Saturday. Former Obama deputy national security adviser Ben Rhodes tweeted at Trump, saying no president can order a wiretap.

"Those restrictions were put in place to protect citizens from people like you," Rhodes said.

Trump's attack against Obama on Saturday wasn't the first time in the past week that Trump accused the former president of working against him. During an interview with Fox News, Trump blamed Obama for being involved in a nationwide wave of protests against his administration's policies and national security leaks.

"I think President Obama's behind it because his people are certainly behind it", he said, adding, "I also think it's just politics."

Trump's relationship with Russia has been heavily scrutinized since he was a candidate. The intelligence community concluded in a report that Russian operatives sought to tip the campaign in Trump's favor through hacks of Democratic officials, including Clinton's campaign manager John Podesta, which were then given and published by websites like WikiLeaks.

Trump has pushed back against any possible influence by the Russians, but his administration has been hit by a number of controversies related to Russia.

Trump's national security adviser, Mike Flynn resigned last month after it was revealed he misled Vice President Mike Pence about his communications with a Russian envoy on sanctions before the inauguration.

Earlier this week, Trump's attorney general, Jeff Sessions, recused himself from any campaign-related cases amid revelations that he did not disclose to senators in a confirmation hearing of his meetings with the same Russian ambassador, Sergey Kislyak, as a senator, during the campaign in which he supported Trump.