Despite initial word of gunshots, Albuquerque's police department said on Twitter that there was "no confirmation" of gunshots. "There is no confirmation that any gunshots were fired, contrary to reports. Possible damage to Convention Center Windows by pellet gun," the department tweeted.

Sasse, the freshman Republican, has emerged as one of Trump's foremost critics from the right. Romney and Sasse have talked, the source said, and Romney encouraged Sasse to seriously consider a run. But Sasse is refusing to enter the race. "We will decline to comment on the senator's conversations," Sasse spokesman James Wegmann said.

The Democratic and Republican presidential front-runners laid out a potential fault line in what would surely to be a heated general election clash after they both swept much closer to closing out their party nominations. Clinton relished a chance to lay into Trump in her victory speech in Philadelphia after winning four out of the five Northeastern primary contests.

The Vermont senator began his bid for the Democratic presidential nomination last year with a sizable financial disadvantage compared to front-runner Hillary Clinton. By the end of last June, Sanders had raised just shy of $14 million for his campaign, less than a third of the $47.5 million Clinton had raised for hers.

Plumes of exhaust steam, a byproduct of heating the main plant at the Yongbyon Radiochemical Laboratory complex, have been seen in commercial satellite images taken March 12 and over the preceding five weeks, the group says. This activity is unusual, the report by the Washington, D.C.-based project, says.

Hours later, Trump reversed his initial position -- criticized as extreme by both supporters and opponents of abortion rights -- saying only the doctors should be held liable. "The Republicans all line up together," Clinton said in an interview with CNN's Anderson Cooper.