Five US States Vote in Key Presidential Primary ElectionsThe key Republican primary elections are in Florida and Ohio, where for the first time in the months-long 2016 presidential campaign, the winner will take all the state's delegates to the party's nominating convention in July. Presidential nominating contests are under way Tuesday in five U.S. states, with the front-runners, Republican Donald Trump and Democrat Hillary Clinton, looking to move closer to winning their parties' nominations, even as their trailing opponents try to curb their momentum. The key Republican primary elections are in Florida and Ohio, where for the first time in the months-long 2016 presidential campaign, the winner will take all the state's delegates to the party's nominating convention in July. In three other contests, Illinois, Missouri and North Carolina, the delegates will continue to be apportioned according to vote counts. Trump, a flamboyant billionaire real estate mogul, has surged to the top of the Republican contest over a one-time field of 17 candidates, now winnowed to three others - Texas Senator Ted Cruz, Florida Senator Marco Rubio and Ohio Governor John Kasich. Political surveys show Trump, who has never held elective office, ahead in four of the states being contested Tuesday, but locked in a tight battle with Kasich in Ohio. Trump's election day got off to a good start when he captured all nine Republican convention delegates at stake from the Northern Mariana Islands, a U.S. territory in the Pacific Ocean. Trump sweep possible Numerous U.S. political analysts say if Trump sweeps all five states, where 358 delegates are at stake, it would make him the likely candidate to capture the Republican nomination. If that happens, he would face the Democratic nominee in the November national election to pick the successor to President Barack Obama, who leaves office next January. Republicans are casting their ballots after several days of angry confrontations at Trump rallies between his supporters and those opposed to his candidacy, with name-calling, pushing, shoving and occasional fist fights. Trump at times has encouraged his supporters to punch protesters and ordered his security staff to quickly remove demonstrators from his rallies, although he has said he wants peaceful campaign events. As voters headed to the polls, Obama deplored the tone of the current campaign, saying he is "more than a little dismayed." He said the "corrosive behavior undermines our society. ... It has to stop." WATCH: Florida voters on primary, candidates No media source currently available ​Without mentioning Trump's name, Obama took a swipe at the campaign of the one-time television reality show host and his disparaging comments about women and Muslims.\n\n"We have heard vulgar and divisive rhetoric aimed at women and minorities, and Americans that don't look like us or pray like us or vote like we do,'' Obama said at an annual luncheon celebrating U.S. friendship with Ireland. Clinton, Sanders Clinton, with a substantial delegate lead over her lone opponent, Vermont Senator Bernie Sanders, is competing with him in the same five states where Republicans are voting. However, the Democratic convention delegates awarded Tuesday will be apportioned according to the vote counts in each state, not on a winner-take-all basis. Clinton, the country's secretary of state from 2009 to 2013, looked ahead to a possible general election match-up with Trump, saying she would confront "the really dangerous path that Donald Trump has laid out." Surveys show Clinton with big leads among Democratic voters in Florida and North Carolina, with closer contests with Sanders possible in Illinois, Ohio and Missouri. Cruz, Rubio Pre-election polling does not suggest that Cruz, a conservative agitator in the halls of Congress, will win any of Tuesday's party primaries, although he says he has the best chance of overtaking Trump because he has beaten him in several other state nominating contests and currently is in second place in the Republican delegate count. U.S. political pundits say Rubio could be forced to quit the race if he doesn't win his home state of Florida, in the country's southeast.