Democratic presidential candidate Hillary Clinton greets supporters as she arrives to speak during a presidential primary election night rally, Tuesday, June 7, 2016, in New York. -AP

WASHINGTON: "Delete your account." Hillary Clinton's snarky tweet Thursday to her White House rival Donald Trump was among the funniest of the campaign. Almost as funny as it was awkward. The message by the 68-year-old former secretary of state-actually written by a young staffer, a Clinton aide told AFP-was in response to the latest broadside by Trump, who had commented on how "Obama just endorsed Crooked Hillary" on Thursday.

"He wants four more years of Obama - but nobody else does!" the presumptive Republican nominee added. When Clinton trolled back, social media exploded. Within two hours her message was retweeted 200,000 times, making it "the most retweeted tweet of the campaign!" according to Clinton's social media director Alex Wall.

With "Delete your account," Clinton, who has struggled to connect with young voters, embraced the quick-witted dry humor of America's millennials. But it also triggered ferocious comebacks from her critics over use of a private email account while she served as America's top diplomat-a scandal she has been unable to shake.

Republicans including Trump have savaged her for her judgment, saying she put US national security at risk, and have accused her of deleting key emails that she did not want Americans to see. "@HillaryClinton, If anyone knows how to use a delete key, it's you," the chairman of the Republican National Committee, Reince Priebus, wrote in a stinging tweet of his own.

Trump, known for his sharp tongue on social media, returned fire against Clinton, mocking her less-than-spontaneous attempt at hipness. "How long did it take your staff of 823 people to think that up-and where are your 33,000 emails that you deleted?" he wrote. Clinton turned over some 30,000 emails to State Department officials after she stepped down from the job in 2013. But she also said she deleted more than 30,000 other emails that were of a personal nature and not related to her work as secretary of state.

Warren on the attack

Sen Elizabeth Warren threw her support behind Democrat Hillary Clinton for president Thursday, following President Barack Obama in sending a signal to progressive voters now backing Bernie Sanders that it's time to unite around the presumptive Democratic nominee.

"I am ready to get in this fight and work my heart out for Hillary Clinton to become the next president of the United States and to make sure that Donald Trump never gets anyplace close to the White House," the Massachusetts senator said on MSNBC's "The Rachel Maddow Show."

Warren was the only holdout among the Senate's Democratic women and, given her stature among liberals, her endorsement could be an important boost for Clinton. She also is being floated as a potential vice presidential pick for Clinton.

Ahead of her endorsement Thursday, Warren spoke to the American Constitution Society and attacked Trump as a "loud, nasty, thin-skinned fraud." Trump "has never risked anything for anyone and serves nobody but himself. And that is just one of the many reasons why he will never be president," Warren said in the scathing broadside also aimed at the top two Republicans in Congress.

The liberal lawmaker increasingly has tangled with Trump, taking on an attack-dog role that she seems able to execute more effectively than other Democrats, including Clinton herself. Trump has lashed back, labeling her "Goofy Elizabeth Warren" and ridiculing her claims to Native American heritage.

Warren took aim at Trump's contention that US District Judge Gonzalo Curiel can't preside fairly over a case involving Trump University because the US-born Curiel is of Mexican descent and Trump wants to build a wall along the border with Mexico.

Senate Majority Leader Mitch McConnell, R-Ky, and House Speaker Paul Ryan, R-Wis, both have strongly condemned those comments, but Warren, D-Mass, argued that McConnell and Ryan are really no better than Trump on the issue of judges. She cited what she contends is McConnell's blockade of Obama's judicial nominees and Ryan's acquiescence in the strategy.