2016 Presidential Candidates Tweak Messages, Schedules After Orlando Shooting

— -- It was supposed to be a turning point in the 2016 presidential race: The first full week of competition between the two presumptive party nominees.

But after the mass shooting in Florida this weekend, which claimed the lives of at least 50 people and injured more than 50 others, there are already signs that the tone and tenor of the campaign this week will be far different than expected.

Senior aides to presumptive Republican nominee Donald Trump, who had promised to deliver a speech on Monday taking on presumptive Democratic nominee Hillary Clinton, said plans had changed.

The speech, which he will give at Saint Anselm College in Manchester, New Hampshire, will "further address this terrorist attack, immigration, and national security," according to a written statement released by his campaign.

Trump said last week the address would cover “all of the things that have taken place with the Clintons. I think you're going to find it very informative and very, very interesting.”

In his statement today, Trump excoriated both Clinton and President Obama, who he said “disgracefully refused to even say the words ‘Radical Islam’” in his remarks at the White House Sunday afternoon.

“For that reason alone,” Trump asserted, “he should step down.”

Trump added that Clinton “wants to dramatically increase admissions from the Middle East, bringing in many hundreds of thousands during a first term -- and we will have no way to screen them, pay for them, or prevent the second generation from radicalizing.”

Meanwhile, the GOP candidate caught blowback for a series of tweets he sent over the course of the day, some of which appeared self-congratulatory.

As for Clinton, who was scheduled to hold her first joint campaign event with Obama in Wisconsin this Wednesday after the president’s endorsement last week, she announced Sunday the appearance would be postponed “because of the tragic attack in Orlando."

Her campaign has not announced further changes to her campaign schedule, and she is set to hold an event in Cleveland Monday.

In her own written statement, the Democratic candidate made no mention of Trump. Instead, she called the slaughter at the gay nightclub in Orlando "an act of terror” and “an act of hate."

"We can say for certain that we need to redouble our efforts to defend our country from threats at home and abroad," Clinton said.

Vermont Sen. Bernie Sanders, who spent the weekend in his home state assessing next steps for his campaign, called the events in Orlando “unimaginable.”

“ISIS must be destroyed,” he told reporters Sunday evening. “We have got to everything humanly possible to prevent these types of tragedies from occurring again.”

The shooter, identified by officials as Omar Mateen, called 911 to pledge his allegiance to ISIS after the shooting began, according to law enforcement officials.

Sanders said Sunday morning on ABC News’ “This Week” that he will likely meet with Clinton Tuesday, the same day the Democratic Party’s nominating process officially comes to a close, with the final primary in Washington, D.C.

ABC’s Meghan Keneally, Corinne Cathcart, David Caplan and Michael Edison Hayden contributed reporting.