"America never stopped being great!" she said to cheers from supporters in Miami.
"It's clear tonight that the stakes in this election have never been higher, and the rhetoric we're hearing on the other side has never been lower."
The road ahead
A new CNN/ORC poll found that both Clinton and Sanders would easily defeat Trump if the general election – set for November 8 – were held now.
But few are likely to underestimate the 69-year-old Trump after his primary rout.
His incendiary rhetoric has infuriated his Republican rivals, and the race has descended in recent days into a mud-slinging match between him and the mainstream favorite Marco Rubio.
The Florida senator sent a letter to his supporters Tuesday calling Trump "a serious threat to the future of our party, and our country."
"In just the last few days, Trump has refused to condemn white supremacism and the Ku Klux Klan, praised dictators Saddam Hussein and Moammar Gaddafi, and proposed infringing upon the First Amendment of our Constitution," he wrote.
"This is no joke. It's time to fight back."
An incendiary campaign
But it might be too little too late, with polls showing Trump with a commanding lead nationwide.
The CNN/ORC poll gave Trump 49% of support nationwide, with Rubio a distant second at 16% and Ted Cruz one point further behind.
Rubio was not projected to win in any of the 11 states that voted Tuesday, fundamentally undermining his claim to be the representative of mainstream Republicanism.
But he ended the day in Florida, a clear signal that he wants to win his own home state, which votes on March 15.
For good measure, his campaign also announced events in Kentucky, Kansas, and Louisiana, in an attempt to pre-empt questions about his future.
Cruz was kept alive with projected victories in his adoptive home state of Texas, with a bumper haul of delegates, and neighboring Oklahoma.
Rubio and Cruz will harbor long-shot hopes that Trump fails to win enough delegate support to secure the nomination outright, leaving the convention to decide the nominee in July.
They may also be betting that whoever emerges strongest from a brutal 2016 campaign would be the prohibitive favorite in four or eight years' time.
Trump's inflammatory rhetoric – he has accused Mexico of sending "rapists" across the border, mocked women and the disabled, urged a ban on Muslims entering the country, and eagerly advocated the use of torture – would have been the undoing of a normal candidate.
But the 2016 cycle has been anything but normal, with a furious electorate keen to back an outsider who scorns the political establishment.
As the prospect of a Trump nomination loomed ever larger, a lengthy clip by British satirist John Oliver skewering his many false claims and inconsistencies has gone viral.
The segment, first aired late Sunday on "Last Week Tonight," launched a hashtag, #MakeDonaldDrumpfAgain, in a nod to the candidate's original family name.
By Tuesday, the word "Drumpf" was ahead of both Rubio and Cruz in Google search rankings – right behind Trump himself. – Andrew Beatty, AFP / Rappler.com