Sanders has been inching there for months now, but he finally dropped the nice-guy routine this week -- and with an only slightly coy hit on knitting together Clinton's fabled speaking fees and her Wall Street connections.
"By the way, without naming any names, Goldman Sachs also provides very, very generous speaking fees to some unnamed candidates," Sanders said, as the crowd chuckled. "Very generous. Now I know that some of my opponents are very good speakers, very fine orators, very smart people, but you gotta be really really, really good to get $225,000 a speech. That's all I'll say."
He obviously did not need to name names; a member of the audience yelled, "It was $600,000!"
His audience didn't seem to mind that the senator, who declared months ago that he wouldn't go negative, was now doing exactly that.
At the top of his speeches Tuesday in Fort Dodge and Carroll, Sanders spoke about the movement and revolution (as he likes to call it) that his campaign is bringing across America, boasting that 450,000 people have come to see his campaign speeches in the past eight months.
"You may hear me say a word or two about my friend Donald Trump but not my Democratic colleagues, who are serious people," Sanders said. He also pointed to the name-calling and candidates "ripping into each other," which seems like a not-so-subtle hit at Trump.
But then only a few minutes later, Sanders criticized Clinton's campaign fundraising tactics and the spending of her super PAC, pointing out that he is proud to not have the support of an official super PAC. At the bottom of his official campaign emails, a note says, "Paid for by Bernie, not the billionaires."
Foreign policy jabs
Sanders sharp tone comes as he has arisen as a serious threat to swipe the Democratic nomination from Clinton. Facing a possible repeat of 2008, Clinton has unloaded on Sanders as well -- painting him as an impractical radical and someone who could ultimately lose the White House for Democrats.
Clinton's latest hit was a letter from top diplomats questioning Sanders' ability
to handle serious international situations, including relations with Iran.
"The stakes are high. And we are concerned that Sen. Sanders has not thought through these crucial national security issues that can have profound consequences for our security," the diplomats wrote in their letter. "His lack of a strategy for defeating ISIS -- one of the greatest challenges we face today -- is troubling. And the limited things he has said on ISIS are also troubling."
At a stop in Underwood, as Sanders took questions from the crowd, one woman pointed out to him that he's taking some heat for "not having foreign policy experience." Sanders' defense rests in the logic that experience does not equal good judgment.
His example? Dick Cheney, who Sanders remarked, "had a hell of a lot of experience, God help us all."
But much like the 2008 election where a fresh-faced senator touted his opposition against the war in Iraq, Sanders reminded the audience of Clinton's voting record on the matter, saying that she dutifully listened to Bush and Cheney and Rumsfeld. "She voted for the war in Iraq, the worst foreign policy blunder in the modern history of the United States of America," he said.
Can attacks backfire?
Mo Elleithee, former communications director for the Democratic Party and a veteran of numerous White House bids, including Clinton's 2008 run, said he doesn't think attacking Clinton will hurt Sanders -- unless he goes too far.
"Unless he crosses a line, I doubt it hurts him. On some level, he wants to be careful, he promises to be something to be different, at a certain point he can take it too far and look like everyone else," Elleithee said.
He added the last two weeks before the Iowa caucuses are when candidates want to excite supporters, but it also "has the potential for backfiring if he looks too typical."