"The Final Five," hosted by CNN and aired from 8 to 11 p.m. ET.
Trump, the GOP's Ted Cruz and John Kasich and Democrats Hillary Clinton and Bernie Sanders are all set to take part in a forum dubbed "The Final Five," hosted by CNN and aired from 8 to 11 p.m. ET.
Donald Trump on Monday has two events that could help determine his future with the GOP establishment. He is meeting with Sen. Tom Cotton and others, then giving a speech to the American Israel Public Affairs Committee, a potentially tough audience that has not yet warmed to Trump.
He pledged Sunday that he'll lay out his plan for a deal between Israel and Palestine, a goal that has eluded leaders for decades. His comments on the subject and session with establishment Republicans could dominate the day.
Meanwhile, the efforts to stop Trump from capturing the Republican nomination kicked into overdrive last week, with conservative leaders huddling in Washington to plot a strategy to stop him that ranged from denying him the delegates he needs to mounting a third-party candidacy.
Why I'm voting for Donald Trump
The forum gives Trump an opportunity to rebut those efforts in front of a national audience -- particularly after a day in which he'll meet with Republican leaders in an attempt to smooth out concerns with his candidacy.
It's also an opportunity to address the topic dominating the political world: the increasingly visible violence at Trump rallies -- where a protester was punched and kicked in the latest incident Saturday.
But the GOP front-runner is taking no responsibility.
"Why are they never the bad people? This is a terrible thing," he said of the protesters who have disrupted his events at the Palm Beach County GOP dinner at his Mar-A-Lago resort in Florida Sunday night.
Can Clinton stay pivoted?
Hillary Clinton dropped her attacks on Sanders and began focusing more on the general election -- and then she lost Michigan, and had to turn her attention back to Sanders.
After five wins last week, Clinton is signaling again that she's turning her focus to Trump, casting him as ill-suited to lead the country.
It's more than an effort to get a head start on defining a general-election foe. If Clinton wins the party's nomination, she faces a serious challenge in turning Sanders' loyal, energetic supporters into backers of her campaign. The harder she hits Sanders, the tougher that job becomes.
If the two don't have much in common, at least they share an enemy. And as Trump grows more controversial -- with liberals increasingly engaging in mass protests and efforts to shut down his events -- taking on Trump could be the best opportunity Clinton has to win over reticent Democrats.
Cruz's religious outreach, take two
Texas Sen. Ted Cruz's initial campaign strategy depended in large part on his ability to win over Evangelical voters in the Deep South.
That didn't happen, as Trump defeated Cruz in most of the region.
Now, though, Cruz has an opportunity to win over another religious group: Mormons.
They play a large role in Tuesday contests in Utah and Arizona. They were also key in Idaho, where Cruz has already won. The Texas senator's success in the west could help him make major delegate gains on Trump.
That's why he could make a major point of emphasizing religious liberty -- a core issue for his campaign since its outset.
"There is an awakening and a spirit of revival -- all across this country, people are waking up," Cruz said Saturday in Provo, Utah.
Sanders and the Democratic base
It's the great irony of the Democratic presidential race: After a year of bashing the establishment, Bernie Sanders' chances of winning the nomination now depend largely on the establishment.
It won't be an easy sell.
After losses in Florida, Illinois, Missouri, North Carolina and Ohio last week, Sanders' path to the nomination -- even if Western states help him narrow the delegate gap -- is exceedingly difficult.
The first step is improving his stock with loyal Democrats -- long-time party supporters, particularly older voters, who have largely supported Clinton.
Sanders on Sunday said that he is "not doing well with older people."
As the Vermont senator implored a rally audience about the importance of young people's involvement in his campaign -- part of his standard stump speech -- he paused a moment and added, "If I can make a political statement here, it's interesting as we go along this campaign, we are not doing well, we are working on it, I cannot tell you why, we are not doing well with older people."
So John Kasich won Ohio and its 66 delegates. What's next?
The Ohio governor's campaign is all about a play for the Republican National Convention in Cleveland -- where he's hoping home-court advantage will help him court unpledged delegates, those committed to Marco Rubio on the first ballot and more to quickly grow his support in a floor fight.
To make it that far without coming under withering pressure to clear the path for Ted Cruz to become the lone Trump alternative, though, he'll need wins.
So Kasich will need to lay out a clear strategy to voters and donors on national television to win states and demonstrate he's not a spoiler.
John Kasich on getting out of the race: 'That's nuts'
It's also worth watching whether Kasich's tone changes. He has stayed above the fray so far, but now, the race is down to three candidates -- with the other two nowhere near being knocked out.
At the center of Kasich's argument: He's the best candidate to defeat a Democrat in November.
He's also likely to make the case that owning the most delegates headed into the convention shouldn't guarantee anything for the Republican front-runner if that candidate falls short of the 1,237 delegates needed to clinch the nomination.
"The Republicans have had 10 conventions like this and only three times has the person going into the convention with the most delegates won," Kasich told CNN's Dana Bash on "State of the Union" Sunday. "And you see when you get to a convention the delegates will take this very seriously."