News Analysis: Trump marches toward nomination, but still stoppable

U.S. Republican front-runner Donald Trump is driving on a fast track all the way to the 2016 presidential nomination after winning key battleground states on Tuesday, but his strong momentum is not unstoppable, experts have said.

Also, they think Trump's loss in Ohio has left the door open to a possible contested Republican convention in Cleveland in July.

RUBIO DROPS OUT

Trump, the brash New York billionaire, scored a crucial win in Florida, where 99 delegates were up for grabs in the biggest prize of the day, knocking out his mainstream party rival Senator Marco Rubio.

The 44-year-old senator suspended his campaign for president after a bruise in his home state where he pinned his rebounce on winning the big winner-takes-all state.

Just like the rise of Trump, the fall of Rubio, who was once a rising star in the party, has also been extraordinary, Allan Lichtman, professor at the American University said in Monday's teleconference with the press.

Rubio just got caught up in the anti-establishment ride and had no clear campaign message, Lichtman said, adding that Rubio "had a huge mistake by going personal, getting down in the gutter with Donald Trump."

The commanding win in Florida gave Trump a very big delegate lead although he lost big winner-takes-all state of Ohio with 66 delegates to another establishment favorite candidate, Governor John Kasich, in his turf.

"It's Ohio then the deep blue sea, frankly, for him. He's going to fall into the ocean. He doesn't really have bright prospects in subsequent primaries," Lichtman said of Kasich.

"Ohio would be Kasich's only win, and that would essentially leave the Republican contest down to a battle between the former reality TV star Trump and Senator Ted Cruz of Texas, with Trump having a big advantage," he said.

CRUZ IS THE ONLY ALTERNATIVE

"A Kasich win is actually good for Trump," Thomas E. Mann, senior fellow in Governance Studies at The Brookings Institution, told Xinhua before Tuesday's make-or-break contests.

"Kasich has a reasonable chance of winning his home state but almost no chance of winning the nomination. The only chance of stopping Trump is for both Rubio and Kasich to drop out of the race and Cruz to face Trump one-on-one," Mann said.

Tuesday's votes indeed represented the last, best chance for establishment Republicans -- leaders of the party, senators, governors, officials of the Republican National Committee -- to stop Trump, an unpredictable and uncontrollable contender whose controversial and rowdy campaign they fear would lead Republicans to defeat in the general elections in November.

Trump has vowed to deport 11 million illegal immigrants, build a wall along the border with Mexico, impose protectionist trade policies and temporarily ban Muslims from entering the country.

He plays on Republicans' anger at their own party and taps into the fear of foreign influence and fear of violence to win over voters with his rhetoric "To Make America Great Again," experts say.

With Rubio forced out and Kasich dangling on life support, the only viable alternative to Trump is Cruz, a Tea Party favorite.

However, the Republican establishment also despises Cruz, who is reviled by many of his Republican colleagues for his role in the 2013 government shutdown.

"It is only with the greatest reluctance, with a clothespin -- they're putting clothespins on their nose -- that the Republican establishment is tilting toward Ted Cruz," Lichtman said.

CONTESTED CONVENTION

Talking about a contested Republican convention, Kasich told supporters at a victory party Tuesday at Baldwin Wallace University in Cleveland that he will not "take the low road to the highest office in the land."

"We are going to go all the way to Cleveland and secure the Republican nomination," said the governor.

A Republican needs to win 1,237 Republican delegates to become the nominee,, who faces Hillary Clinton or Bernie Sanders. If no candidate reaches that threshold by the close of the last primary on June 7, the party convention will almost certainly be contested, a scenario which is extremely rare in modern history.

"The plan (of Kasich) is to win Ohio, and some other states, and if that happens, nobody is going to have enough delegates to win the nomination on the first ballot," John Weaver, Kasich's chief campaign strategist, has said. Kasich's supporters had believed that an Ohio win would give his bid its first real momentum, attracting donors and endorsements.

Unlike the old-line party bosses, the party establishment nowadays can't swing delegates, as none of the establishment officials have delegates in their pocket. "So the best they can do is help with fund-raising, help with endorsement, help with campaigning," Lichtman said.

Mainstream Republican Party figures have spoken out against Trump, after an outbreak of violent scuttles between his supporters and protestors that forced him to cancel a Chicago rally last week, and scattered protests at some of his campaign events this week.

House Speaker Paul Ryan, who will preside over the GOP convention in July, has so far stopped short of weighing in on the developments in the national race. Though he has publicly admonished Trump's message three times now, he said earlier Tuesday that he still planned to support the eventual Republican nominee for president no matter who he is.

If Trump is coming in with a clear lead, the Republican Party would not deny the popular choice of the nomination, Lichtman said. While if the GOP denies Trump the nomination, "it's going to rip the party apart and it may even lead to Donald Trump running on a third-party campaign," the professor predicted. Endi