President Trump ratcheted up his attacks on his predecessor Saturday, with his allegation that former President Obama ordered surveillance of the real estate mogul before the November election sparking confusion and backlash.

Democrats slammed Trump for making the accusations without offering evidence, characterizing his early morning rant as an effort to distract from renewed scrutiny of his aides and allies' alleged ties to Russia.

Taking to Twitter early in the morning, Trump fired off claims — without providing evidence — that Obama had wiretapped his phones in Trump Tower in New York to monitor his campaign’s communications.

In the tweets, Trump compared the move to McCarthyism, the draconian hunt for communists in the U.S. government in the 1940s and '50s, and Richard Nixon’s ordered wiretapping in the 1970s Watergate scandal.

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“How low has President Obama gone to tapp [sic] my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!” Trump wrote in one tweet.

“Terrible! Just found out that Obama had my ‘wires tapped’ in Trump Tower just before the victory. Nothing found. This is McCarthyism!” he said in another.

A spokesman for Obama denied the accusations, saying that no one in Obama's White House ordered the surveillance of Americans, let alone Trump.

"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," spokesman Kevin Lewis said in a statement.

At least two Republicans, Sen. Ben Sasse (Neb.) and Rep. Justin Amash Justin AmashOn The Trail: How Nancy Pelosi could improbably become president History is on Edward Snowden's side: Now it's time to give him a full pardon Trump says he's considering Snowden pardon MORE (Mich.), called on Trump to provide more information about his allegation.

“We are in the midst of a civilization-warping crisis of public trust, and the President’s allegations today demand the thorough and dispassionate attention of serious patriots," Sasse said in a statement.

Sasse noted any such wiretap would have taken place with authorization from the Foreign Intelligence Surveillance Court and "an application for surveillance exists that the court found credible."

"The president should ask that this full application regarding surveillance of foreign operatives or operations be made available, ideally to the full public, and at a bare minimum to the U.S. Senate," Sasse said.

Former Obama adviser Ben Rhodes slammed Trump over the allegation, tweeting, "No President can order a wiretap. Those restrictions were put in place to protect citizens from people like you."

House Minority Leader Nancy Pelosi (D-Calif.) labeled Trump the “Deflector-In-Chief" for his tweets, while former Obama adviser David Axelrod said Trump "kicking up dust only adds to suspicions and the need for full public reckoning."

“Mr. President: If there was a wiretap at Trump Tower, that means a fed judge found probable cause of crime which means you are in deep sh--,” Rep. Ted Lieu (D-Calif.) wrote on Twitter.

Trump’s allegations appeared to blindside officials in his own administration. A senior Trump official reportedly told NBC News on Saturday that neither he, nor other administration officials, seemed to know what the president was talking about.

Observers speculated that Trump may have been reacting to a Breitbart News story published Friday. That story quoted conservative radio host Mark Levin alleging that the Obama administration used “police state” tactics to keep tabs on the real estate mogul’s presidential campaign.

The article has been making rounds among Trump’s White House staff, according to The Washington Post. One White House official told the Post the Breitbart report provided a useful list for tracking alleged attempts by the Obama administration to undermine Trump.

Republican Sen. Lindsey Graham Lindsey Olin GrahamSenate Republicans signal openness to working with Biden Loeffler calls for hearing in wake of Netflix's 'Cuties' Quinnipiac poll shows Graham, Harrison tied in South Carolina Senate race MORE (S.C.) expressed unease about Trump’s remarks Saturday while also suggesting it would be troublesome if the Obama administration had a lawful reason to monitor Trump’s communications.

“I’m very worried that our president is suggesting the former president has done something illegal,” Graham said at a town hall in Clemson, S.C.

“I’d be very worried if in fact the Obama administration was able to obtain a warrant lawfully about Trump campaign activity with foreign governments,” he continued. “It’s my job as United States senator to get to the bottom of this."

Trump's tweets Saturday represented a further souring of his relationship with his predecessor, after the pair described a warmer transition process following a bitter campaign.

The wiretapping allegation followed Trump claiming last month that Obama was behind the wave of protests and government leaks that have marked the early days of his administration. Trump also argued in news conference last month that he "inherited a mess" from Obama, suggesting that his predecessor was responsible for foreign and domestic policy disasters and massive unemployment in the U.S.

Trump's allegation Saturday invoking Watergate was punctuated with the president firing off a tweet needling actor Arnold Schwarzenegger's decision to quit as the host of "Celebrity Apprentice," with Trump saying his successor on the show was "fired" by ratings. Trump also appeared slated to go golfing Saturday at his private Mar-a-Lago club in Florida, according to a pool report citing the White House press office.

Trump’s young administration has been roiled by questions about his potential ties to Russia, and what role the Kremlin played in the 2016 election.

The U.S. intelligence community concluded last year that Moscow ran an extensive influence campaign to help Trump’s presidential bid, while scrutiny of his team's contacts with Russian officials during the campaign and before he took office has mounted.

The president’s first national security adviser, Michael Flynn, resigned last month amid revelations that he misled Vice President Pence about his discussion of U.S. sanctions on Russia with Moscow's ambassador to the U.S., Sergey Kislyak, before Trump took office.

Kislyak’s name re-emerged in headlines on Wednesday night, when The Washington Post reported that Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsTrump's policies on refugees are as simple as ABCs Ocasio-Cortez, Velázquez call for convention to decide Puerto Rico status White House officials voted by show of hands on 2018 family separations: report MORE had twice spoken with the ambassador during Trump’s presidential campaign.

Sessions, facing mounting pressure from Democrats and some Republicans, announced Thursday he would recuse himself from any federal investigations into Russia's intervention in the election.

Democrats slammed Sessions over his conversations with the Russian envoy, noting that it appeared to contradict his testimony during his confirmation that he didn't have contact with Russian officials.

The former Republican Alabama senator denied that he spoke to the Russian official as a surrogate of Trump's campaign and denied he intentionally misled senators, adding he couldn't “recall any specific political discussions” with Kislyak.

Updated: 9:54 p.m.