John Kasich has decided to suspend his presidential campaign after struggling to gain traction against Republican front-runner Donald Trump.
The Ohio governor did not have a path to secure the nomination outright, but pledged to lobby for his candidacy during the Republican convention in July.
Donald Trump holds a commanding lead and is closing in on the nomination.
Despite being a popular governor, John Kasich only won his home state.
Texas Senator Ted Cruz dropped out of the race on May 3 after losing to Donald Trump in the Indiana primary.
John Kasich canceled events in Washington and announced an evening event in his home state on May 4.
Earlier, John Kasich released a Star-Wars themed advert describing himself as the “only hope” against Donald Trump.
Blocking from winning the nomination outright, John Kasich and Ted Cruz had hoped to force a contested convention, in which party officials, not voters, choose for the nominee.
Now it is all but certain Donald Trump will have the 1,237 delegates needed to become the nominee before the July convention in Cleveland, Ohio.
John Kasich had been widely seen as the most moderate and electable Republican candidate and polled well against Hillary Clinton, the likely Democratic nominee.
However, John Kasich’s general election strength did not garner him enough support among Republican primary voters.
The Ohio governor promoted an optimistic message while campaigning, shunning negative attacks against other candidates.
Florida Senator Marco Rubio, who dropped out in March, garnered more delegates than John Kasich during primary elections.
Ted Cruz and John Kasich had announced an alliance to stop Donald Trump and “to ensure that we nominate a Republican who can unify the Republican Party and win in November” prior to the Indiana, New Mexico and Oregon state primaries, but that quickly crumbled.
Republicans are now divided over whether to support Donald Trump as the Republican nominee.
John Kasich’s name has been floated as a possible vice presidential pick but he has denied that he would accept a nomination.
Republican presidential hopefuls Ted Cruz and John Kasich have announced they will now co-ordinate strategies against rival Donald Trump.
Ted Cruz has said he will cut campaigning in the Oregon and New Mexico primaries to help John Kasich, while the latter will give Ted Cruz a “clear path” in Indiana.
Donald Trump responded to his rivals saying they were “totally desperate” and “mathematically dead”.
The New York businessman has a clear lead in delegates but may still fall short of the 1,237 needed to win outright.
If Donald Trump does not reach the target, the vote will go to a contested convention – where a different nominee may emerge through negotiations among party figures.
John Kasich and Ted Cruz announced their move in near-simultaneous statements.
Ted Cruz’s campaign manager, Jeff Roe, said: “Having Donald Trump at the top of the ticket in November would be a sure disaster for Republicans. Not only would Trump get blown out by [Hillary] Clinton or [Bernie] Sanders, but having him as our nominee would set the party back a generation.”
John Weaver, John Kasich’s strategist, said in a statement released on the candidate’s site: “Our goal is to have an open convention in Cleveland, where we are confident a candidate capable of uniting the party and winning in November will emerge as the nominee.”
Some Republican strategists have been urging this deal for weeks but analysts say it may now have come too late to stop Donald Trump.
In response, Donald Trump tweeted: “Wow, just announced that Lyin’ Ted and Kasich are going to collude in order to keep me from getting the Republican nomination. DESPERATION!
“Lyin’ Ted and Kasich are mathematically dead and totally desperate. Their donors & special interest groups are not happy with them. Sad!”
Donald Trump has frequently said the GOP nomination process is “rigged” to favor establishment figures against him.
However, the Republican frontrunner did last week promise to change his image, in a closed-door meeting with GOP leaders.
The Indiana primary is on May 3, Oregon is on May 17, with New Mexico on June 7.
However, before those comes voting in five north-eastern states where Donald Trump is heavily favored.
Maryland, Rhode Island, Connecticut, Pennsylvania and Delaware all vote on April 26.
Campaigning in Maryland on April 24, Donald Trump said he was confident of avoiding a contested convention.
On the Democratic side, Bernie Sanders spoke to a rally of 14,000 supporters in New Haven, Connecticut, on April 24, again accusing rival Hillary Clinton of earning money through “speeches behind closed doors on Wall Street”.
Hillary Clinton retains a clear lead in delegates and will hope the north-eastern state votes will effectively put an end to Bernie Sanders’ dogged campaign.
Bernie Sanders and Hillary Clinton have traded increasingly hostile remarks in recent weeks.
However, Democratic National Committee chairwoman Debbie Wasserman Schultz said: “Regardless of the intensity of what’s played out here… we are going to be unified.”
Donald Trump has won a decisive victory in the key state of Florida but lost to John Kasich in Ohio.
In the Democratic field, Hillary Clinton extended her lead with wins in Florida, Ohio, Illinois and North Carolina.
Meanwhile, Marco Rubio dropped out of the Republican race after losing in his home state of Florida to Donald Trump.
Donald Trump has also won in Illinois and North Carolina.
The billionaire’s victories cause a headache for the Republican Party because many senior members are concerned by his policies and tone.
Donald Trump will need just over half of the hundreds of delegates remaining to win a majority in the Republican race and assure him of the nomination.
Five big states on Tuesday chose their preferred candidate for November’s presidential election.
The winners for both parties in Missouri are yet to be called with Hillary Clinton locked in tight competition with challenger Bernie Sanders and Donald Trump fighting Ted Cruz.
“We have to bring our party together,” Donald Trump said in Palm Beach, Florida, as the results came in on Tuesday evening.
However, John Kasich secured his first win in the Republican contest in the state of Ohio where he is governor.
In his victory speech, John Kasich said he wanted to create a “climate of opportunity” for future generations and praised the campaign of Marco Rubio.
Earlier Marco Rubio announced he was suspending his campaign on stage in Miami.
He said the US was in the middle of a “political storm”, and voters were angry and frustrated.
In Florida, Hillary Clinton gave an upbeat victory speech in which she chastised Donald Trump and said “Americans were hungry for solutions”.
She listed student debt, affordable childcare and inequality as issues she pledged to address.
Florida and Ohio are particularly important in the race for the Republican nomination because the winning candidate gets all of the delegates on offer – 99 in Florida and 66 in Ohio.
Those delegates go to the national convention in July where the presidential nominee will be chosen.
However, Donald Trump’s latest victories come amid increasing condemnation of his campaign within the Republican Party, and after a string of violent incidents at his rallies.
Some senior Republicans have said they would never support him, and on March 15 it emerged that a group of leading conservatives are planning ways of stopping Donald Trump from winning the Republican nomination – including rallying around a third-party candidate.