Mr Trump posted his tweet before the caucuses were called in earnest, but after Fox News had weighed in to project Mr Sanders as the winner.
At the time, results from less than 5 per cent of the precincts in the Silver State were accounted for, but the president wasted no time before weighing in on the race.
"Looks like Crazy Bernie is doing well in the Great State of Nevada. Biden & the rest look weak, & no way Mini Mike can restart his campaign after the worst debate performance in the history of Presidential Debates," Mr Trump wrote in a message referring to Mr Sanders, Joe Biden and billionaire Michael Bloomberg, who made his debate debut in Nevada this week but did not participate in Saturday's caucuses.
Then in an apparent nod to the resistance he and Mr Sanders have both faced as outsider candidates, Mr Trump offered some quick advice: "Congratulations Bernie, & don’t let them take it away from you!"
Even before a victor was announced, Mr Sanders had been attacked repeatedly by pundits on MSNBC, where one anchor, Chris Matthews, likened the Vermont senator's political ascension to the fall of Paris to the Nazis during the Second World War.
The reaction to the surging Sanders campaign is reminescent of Mr Trump's 2016 campaign, when he was widely panned by mainstream news outlets and written off as a non-serious candidate, if not simply political entertainment. Both men have also reportedly been targeted by the Russian government, with recent headlines indicating Mr Sanders had been informed that country was intent on helping his candidacy.
Mr Trump won the Republican Nevada caucuses in 2016, when he faced a party establishment that he slowly forced into submission as he continued to win primary states that year. Mr Sanders lost to Hillary Clinton in the Nevada Democratic caucuses that year.