Sen. Elizabeth Warren (D-MA) has been absent from the campaign trail of late as one of Hillary Clinton's most powerful surrogates. But on Wednesday morning, she hit Donald Trump where it hurts him even more: Twitter. In a series of tweets, Warren ridiculed Trump's insistence that the 2016 election is "rigged" against him, calling him a "sore loser" and urging him to put on his "big-boy pants." The tweetstorm served as a preamble to an op-ed Warren penned for the Washington Post in which she argues that Trump alone is not responsible for spreading the "myth" of rigged elections. Instead, she says his latest claims are "just one more symptom of a long-running effort by Republicans to delegitimize Democratic voters, appointees and leaders."