Former secretary of state Hillary Clinton on Wednesday questioned whether her rival in the Democratic presidential primary, Sen. Bernie Sanders (Vt.), is qualified to be president.

"I think he hadn't done his homework and he'd been talking for more than a year about doing things that he obviously hadn't really studied or understood," Clinton said in an interview on MSNBC's "Morning Joe," just one day after losing the Wisconsin primary to Sanders, "and that does raise a lot of questions."

Clinton's comments follow a New York Daily News interview with Sanders that critics say revealed his inability to explain specifically how he would accomplish goals such as breaking up the biggest banks.

Clinton, who will next face off against Sanders in the April 19 primary in New York, also questioned his commitment to the Democratic Party. Sanders has always caucused with Democrats in Congress but is an independent, and has described himself as a democratic socialist. In recent days, her campaign has emphasized how both she and her husband, former president Bill Clinton, have worked to support Democratic candidates for decades.

Bernie Sanders told reporters of a recent spat with Hillary Clinton, "If I'm going to be attacked for being 'unqualified,' I will respond in kind.'" (Reuters)

The argument over who is or is not a Democrat is aimed primarily at elected Democrats, party leaders and activists, many of whom are already backing Clinton. As Sanders's campaign has started talking about "flipping" Clinton delegates, she and her surrogates have begun to question Sanders's commitment to the Democratic Party and to other elected leaders. Clinton supporters note that Sanders has not raised money for the party.

"I think he himself doesn't consider himself to be a Democrat and, you know, look, he's raised a lot of important issues that the Democratic Party agrees with, income inequality first and foremost, but it's up to the Democratic primary voters to make that assessment," she said of Sanders. "I've been in the trenches for a long time and I believe in electing Democrats up and down the ticket. I want to see the United States Senate move back into Democratic hands with my friend Chuck Schumer as the majority leader."

Clinton had a similar assessment in an interview published Wednesday. Asked whether Sanders is a "real Democrat," Clinton first hedged, but then made clear she has doubts.

“Well, I can’t answer that,” she said in the Politico interview conducted last week. “He’s a relatively new Democrat, and, in fact, I’m not even sure he is one. He’s running as one. So I don’t know quite how to characterize him.”