Clinton, Sanders race in New York takes on a tougher tone

With a pledged delegate lead of more than 250, Clinton remains the favorite to capture the party's nomination.

The Democratic party officials who can back either candidate overwhelmingly support Clinton by a margin of 469-31 according to an AP count.

Isabel Framer, a judicial interpreter and DNC member from Ohio, said she received a threatening message at her office several weeks ago, calling her support for Clinton "crap."

Tad Devine, a senior Sanders adviser, said the campaign has not encouraged its supporters to take any aggressive tactics in promoting the senator.

Campaigning in New York City on Monday, she questioned his foreign policy credentials, support for immigration reform and likened his record on gun control to that of the National Rifle Association.

"There seems to be a growing level of anxiety in that campaign which I hope doesn't spill over into the way that his supporters treat other people who have every right to support whomever they chose," she told reporters after a campaign stop in Queens.

In New York, where Gov. Andrew Cuomo banned fracking in 2014, Sanders portrays Clinton as working in unison with oil and gas companies to push fracking around the globe while she served as President Barack Obama's secretary of state.