But Bernie Sanders has also refused to concede the race and the Democratic National Committee has yet to acknowledge Clinton as the party's nominee — unlike its counterpart on the other side of the aisle.
"We congratulate both Hillary Clinton and Bernie Sanders for finishing strong today in the District of Columbia," DNC chairwoman Debbie Wasserman Schultz said in statement Tuesday night after Clinton won the final primary of the year in Washington, D.C.
"Now that our 2016 primaries are officially at their end, Democrats are ready to unify and take on both Trump and the Republican Party that he represents. At our convention in July, we're going to nominate a qualified, capable candidate who will build on the hard-won progress of the last seven years," she added.
Not included anywhere in Wasserman Schultz's statement: Who that nominee will be.
Asked by NBC News' Chuck Todd Tuesday if the party considered Clinton their presumptive nominee, Wasserman Schultz replied, "we are not presuming anything."
After Ted Cruz dropped out of the GOP presidential primary in early May, Republican National Committee Chair Reince Priebus laid down a marker."@realDonaldTrump will be presumptive @GOP nominee, we all need to unite and focus on defeating @HillaryClinton," he wrote on Twitter.
That came much to the chagrin of John Kasich, who was still in the race, despite having no mathematical path to victory. Kasich dropped out shortly thereafter.
Why the difference?
Kasich won just a single state — his home of Ohio — and a total of about 4 million votes out of close to 30 million that were cast.
Sanders lost by a significant margin, but still won the support of a wide swath of the Democratic Party's base. He earned 12.3 million votes to Clinton's 16 million and about 45 percent of pledged delegates.
That puts him in weak position to be issuing demands, as he did Tuesday, but it nonetheless means he needs to be handled more carefully than Kasich, for instance.
Party leaders have gone to lengths to make Sanders feel appreciated over the past week, as they are eager to enlist his support in bringing those 12 million voters into the fold in November. Most will or already have come around, but his hardest core supporters, already skeptical of the DNC, would chafe at attempts to get ahead of Sanders.
As the primary process wound down, the party debated internally how it would handle Clinton's victory if Sanders stayed in the race. "Our focus is on having an inclusive process," said one Democratic party official last week as they navigated the media's declaration that Clinton had won the primary. "We continue to build the infrastructure for the general that would be valuable [for] any nominee."
Nominees typically move quickly to take over the party apparatus and insert their own operatives to run its organization. But Sanders' decision to stay in the race has delayed that, past California's primary last week, and now past the final race of the entire primary season.