DES MOINES, Iowa (AP) — Sen. Bernie Sanders says Hillary Clinton's presidential campaign has decided to "go negative" against him after his recent string of primary season victories, and he's exhorting her to "get back to the issues."

Appearing in a nationally broadcast interview Friday, Sanders defended speaking out harshly against Clinton, saying "we've got to fight back" against statements that she's made.

Sanders was on MSNBC's "Morning Joe" show the day after his wife, Jane, told the cable channel that "Bernie has moved on" from a controversy this week in which he said the Clinton camp suggested he was unqualified to be president.