President Donald Trump on Sunday called on Democrats to launch an investigation into whether Russia helped Sen. Bernie Sanders of Vermont win Saturday's Democratic caucuses in Nevada.

"Are any Democrat operatives, the DNC, or Crooked Hillary Clinton, blaming Russia, Russia, Russia for the Bernie Sanders win in Nevada," the president asked in a tweet.

On ABC's "This Week" earlier Sunday, the White House national security adviser, Robert O'Brien, argued that Russian operatives were most likely working to elect Sanders, the Democratic frontrunner.

O'Brien, however, denied reports that US intelligence believed Russia was working to help Trump's reelection campaign.

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President Donald Trump on Sunday sarcastically suggested that Democrats might conduct an investigation into whether Russia was involved in the victory by Sen. Bernie Sanders of Vermont in the Nevada caucuses.

"Are any Democrat operatives, the DNC, or Crooked Hillary Clinton, blaming Russia, Russia, Russia for the Bernie Sanders win in Nevada," Trump tweeted Sunday, going on to mention the special counsel Robert Mueller's Russia investigation. "If so I suggest calling Bob Mueller & the 13 Angry Democrats to do a new Mueller Report, Democrat Edition. Bob will get to the bottom of it!"

The White House national security adviser, Robert O'Brien, earlier Sunday denied reports that US intelligence believed Russia was working to help Trump's reelection campaign and instead argued that the country was working to help boost Sanders' White House bid.

"There are these reports that they want Bernie Sanders to get elected president — that's no surprise," O'Brien said about the newly cemented Democratic frontrunner, who won big in the Nevada caucuses on Saturday. "He honeymooned in Moscow."

"The president," he added, "has rebuilt the American military to an extent we haven't seen since Ronald Reagan, so I don't think it's any surprise that Russia, or China, or Iran would want somebody other than President Trump."

O'Brien said Trump was going to continue to strengthen US foreign and defense policy. He made the comments to George Stephanopoulos on ABC's "This Week."

Last week, The New York Times reported that Shelby Pierson, a national intelligence aide, delivered a briefing before House Intelligence Committee lawmakers that said the intelligence community had information that Russia was working to help reelect the president in November.

The news drew the ire of Republicans and Trump, who for the first few years of his presidency battled allegations that he had colluded with Russia to win the 2016 election. The special counsel's investigation gave a detailed summary of Russian election interference but found no evidence that the Trump campaign illegally conspired with the Russians.

Stephanopoulos pressed O'Brien on the idea that Russia was working to reelect Trump. Asked whether he'd reviewed reports on pro-Trump support from Russia, O'Brien said, "I have not seen that and I get pretty good access."

"I haven't seen any intelligence that Russia is doing anything to attempt to get President Trump elected," he continued. "I think this is the same old story we've heard before. I've seen the reports from that briefing on the intel committee. I wasn't there, but I've seen no intelligence that suggests that."

The Washington Post on Friday reported that US intelligence officials also told the Sanders campaign that intelligence suggested Russia was working to help him secure the Democratic Party's nomination, though the scope of any such an operation is unclear.

"Let's be clear: The Russians want to undermine American democracy by dividing us, and unlike the current president I stand firmly against their efforts and any other foreign power that wants to interfere in our election," Sanders said in a statement following the Post report.

Sanders suggested at Wednesday night's Democratic presidential debate that some of the nasty posts on social media that have been attributed to his supporters may have actually the result of Russian involvement. He has often received criticism for his more passionate supporters, sometimes called "Bernie Bros." Recently, the Vermont senator faced criticism over reports his followers attacked members of Nevada's Culinary Workers Union after it criticized his "Medicare for All" platform.

The president, meanwhile, replaced his acting director of national intelligence Joseph Maguire, whose aide delivered the House Intelligence Committee briefing about the suspected 2020 Russian meddling. Trump had reportedly been particularly angry because Democratic Rep. Adam Schiff of California was present at the briefing. Schiff led Trump's impeachment in the House last year.

Maguire was replaced by Richard Grenell, the US ambassador to Germany who has been an outspoken Trump supporter.

As NPR reported, the president on Sunday congratulated the Vermont lawmaker on his Saturday-night victory in the Nevada caucuses.

"Bernie is looking more and more like he'll be the nominee unless they cheat him out of it," Trump said as he was leaving the White House for a two-day trip to India.