Over the last 48 hours, the Democratic race for president has descended into a place it had hardly ever gone: the land of invective.

Former Secretary of State Hillary Clinton and Vermont Sen. Bernie Sanders continued a war of words Thursday. Sanders repeated his assertion that she is unqualified to be president because as a senator she voted for the Iraq war, "one of the biggest blunders in U.S. history"; backed most free-trade agreements that cost U.S. jobs; and raised millions in campaign money from Wall Street.

He said he was defending himself because Clinton had said he was unqualified. She never used that word, but her sharp criticism of his proposals as vague and unworkable seemed to him to make much the same point.

"If Secretary Clinton thinks that I just come from the small state of Vermont, that we're not used to this . . . well, we'll get used to it fast. I'm not going to get beaten up; I'm not going to get lied about. We will fight back."

Though the tone of the Democratic campaign has shifted before the pivotal New York and Pennsylvania primaries, it still doesn't compare with the insult-fest in the Republican race. Donald Trump has disparaged "Lyin' Ted" Cruz (not to mention Cruz's wife) and "Little Marco" Rubio and called other former rivals "low-energy," idiots, and losers. Rubio memorably responded by mocking Trump's "small hands."

Sanders on Thursday defended his criticism of Clinton's qualification to be president as a response to her attacks on him, and vowed to keep pushing back as the campaign enters its next phase.

"They think we're not going to fight back? Well, guess again," Sanders said in a Philadelphia news conference Thursday morning before his appearance at the state AFL-CIO convention. "This campaign will respond."

He said he blasted Clinton's qualifications Wednesday night during a rally at Temple University - with an overflow crowd of more than 10,000 - because of a Washington Post headline that said she had attacked his qualifications, and in response to a CNN report that Clinton's campaign strategy in the New York and Pennsylvania primaries is to "disqualify and defeat" Sanders, then unify the party.

During appearances Wednesday in Philadelphia, Clinton said Sanders had vague and unrealistic proposals and did not seem to understand how he would implement his promises.

Her campaign has said she never called Sanders unqualified; she did say Sanders' explanations of some stances "raise a lot of questions."

"Maybe the American people might wonder about your qualifications, Madam Secretary, when you voted for the war in Iraq, one of the biggest blunders in U.S. history," Sanders said Thursday. "The American people might want to wonder about your qualifications when you've supported nearly every trade agreement." He added that Clinton's "spending enormous amounts of time raising money for your super PAC from the richest people in the country" also raises questions about her fitness for the Oval Office.

The exchanges mark a departure from Sanders' generally issue-oriented campaign style. He famously said in an early debate that people were tired of hearing about Clinton's "damn emails."

That was closer to the tone Sanders took Thursday before an AFL-CIO audience of 700, who gave him standing ovations at the Sheraton Downtown as he called for raising the minimum wage and expanding the Affordable Care Act, and derided past trade agreements as job-killers for working people in states like Pennsylvania and Vermont. He barely mentioned his opponent.

That pleased John Hudzynski, executive vice president of AFSCME's District 1199C, which supports Clinton. "I always love what Bernie says. Free education, free everything," he said. "It's great. Everything he says is great, but how do we pay for it?"

Hudzynski said that if Sanders had disparaged Clinton's qualifications in front of the union audience, "he probably would have been booed."

Sanders has repeatedly said he wants to run a positive race, and has declined opportunities in several debates to attack Clinton for the FBI investigation into her use of a private email server as secretary of state, as well as questions about money raised by her family's foundation.

Still, in a wide-ranging interview Wednesday with Inquirer and Daily News journalists, Sanders brought up those issues.

Asked if his campaign might push his party too far left to win in November, Sanders said Republicans were sure to attack Clinton in any event.

"I have not talked about the Clinton Foundation. I suspect that it's quite possible the Republicans may. I have not talked about the FBI and emails, but it is quite possible the Republicans may," he said. "In fact, it's about 100 percent possible."

215-854-2718 @tomfitzgerald