Trump warns of 'riots' if denied nomination

Donald Trump warned on Wednesday of riots if he is denied the Republican presidential nomination, after adding to his growing pile of primary wins, but losing in the key state of Ohio.

A woman shows off her signed campaign poster after a Hillary Clinton r ally in Marshalltown.

Trump and Democrat Hillary Clinton emerged from the "Titanic Tuesday" contests in five states as their party's clear front-runners, but the billionaire real estate mogul's failure to sweep the races means he may fall short of the delegates needed to win the Republican nomination outright.

After the most divisive US campaign in nearly half a century, one that has shattered all rules of decorum and aroused an angry electorate, it remains unclear whether Trump can unite his party in time for the Republican convention in Cleveland in July.


Top Republican power brokers are still manoeuvring to derail Trump, seen as an outsider who hijacked the party primaries, and are looking to a so-called brokered convention which can occur if no candidate wins a majority of delegates by June - as their likely last chance.

But that extraordinary scenario - in which the party would seek to override the outcome of the primaries and unite around an alternative candidate - is a long shot few in the party seem to have the stomach for.

"If Trump has hundreds more delegates than the runner-up... it will be exceedingly difficult to deny him the nomination. In fact, to do so would be to guarantee a meltdown of historic proportions in Cleveland," said Sabato's Crystal Ball, a newsletter by a group of US political scientists.

By far the more probable outcome is for the candidate with the most votes - in all likelihood Trump - to be voted in as the White House nominee following a round of deal-making in the run-up to the convention.