U.S. Special Counsel Robert Mueller's conclusion that Donald Trump did not collude with Russia to win the presidency in 2016 gives the president a powerful weapon to use against his Democratic opponents and a potential boost to what is shaping up to be a tough bid for re-election in 2020.

Mueller's conclusion that neither Trump nor his aides conspired with Russia in 2016 takes away a central charge that Democrats have flung at Trump for two years — that he did not win the presidency fairly or cleanly. The allegations have played out on an endless loop on cable TV news shows, overshadowing Trump's presidency from day one.

Democrats have vowed to continue congressional investigations into the 2016 election campaign and Trump's business practices. But without the solid foundation of a Mueller report that found evidence of any crimes by the president, they now risk seeming to overplay their hand.