Campaigning for the Republican nomination at November's U.S. presidential election took a nasty turn on Wednesday with billionaire businessman Donald Trump accusing rival Ted Cruz of fraud as the field of candidates narrowed ahead of next week's New Hampshire primary.
Rand Paul, a U.S. senator from Kentucky with a libertarian philosophy, pulled out of the Republican race and CNN said conservative Rick Santorum also was quitting.
Both candidates did poorly in Monday's Iowa caucuses, which were dominated by conservative Cruz's defeat of Trump, who has courted controversy by urging a ban on Muslims entering the United States and branding Mexican immigrants as criminals.
The real estate mogul on Wednesday accused Cruz, a U.S. senator from Texas, on Twitter of stealing his victory in Iowa. Cruz's team hit back by telling Trump to seek help for addiction to the social media site.
The two men are going head-to-head for voters in New Hampshire, where Cruz's evangelical Christian credentials will not be as helpful as they were in Iowa. Trump holds big leads in opinion polls of Republicans in New Hampshire.
Former reality TV star Trump called for the nullification of Cruz's Iowa victory or a new vote in the state, which holds the first nominating contest in the presidential election.
"Ted Cruz didn't win Iowa, he stole it," Trump said in a series of tweets. "That is why all of the polls were so wrong and why he got far more votes than anticipated. Bad!"
Trump referred to an email that Cruz's campaign sent on Monday that implied another Republican candidate, Ben Carson, was about to drop out of the race and that his Iowa backers should be urged to vote for the Texan instead. Cruz later apologized for the email.
Trump also accused Cruz's team on Twitter of sending out a mailer designed to look like an official electoral document to scare Iowa voters into turning out at the caucuses.
The Cruz campaign said Trump was just clamoring for attention after the senator came from behind in the polls to beat him on Monday.
"Reality just hit the reality star - he lost Iowa and now nobody is talking about him, so he's popping off on Twitter," Cruz spokesman Rick Tyler said in a statement. "There are support groups for Twitter addiction, perhaps he should find his local chapter."
A Tea Party fiscal hawk, Cruz won support in Iowa from much of the same conservative Christian constituency that helped Santorum to victory in the Iowa caucuses during the 2012 presidential campaign.
Santorum, a former U.S. senator from Pennsylvania, has failed to take off in this campaign. CNN, citing unidentified sources, said he planned to suspend his run for the White House later on Wednesday and would endorse another candidate.
Earlier on Wednesday, Paul became the second Republican to drop out of the race since the Iowa caucuses, behind former Arkansas Governor Mike Huckabee.
"It's been an incredible honor to run a principled campaign for the White House," he said in a statement. "Today, I will end where I began, ready and willing to fight for the cause of Liberty."
Polls in recent days had shown him with about 2 percent support heading into Tuesday's New Hampshire primary. It is not clear which candidate might attract Paul's supporters but Ohio Governor John Kasich said he favored some of Paul's positions, such as his criticism of government electronic surveillance and U.S. intervention abroad.
"If somebody were to ask me about some of the issues on surveillance, I would say that, you know, I think Rand Paul's had some good things to say about it," he told NBC News. "You know, when it comes to the use of military force, I don't want to be policeman of the world."
(By Amy Tennery and Doina Chiacu; Additional reporting by Susan Heavey in Washington and Emily Stephenson in New Hampshire; Writing by Alistair Bell; Editing by Bill Trott; For more on the 2016 presidential race, see the Reuters blog, "Tales from the Trail" http://blogs.reuters.com/talesfromthetrail/; Click here for a graphic on 2016 candidates and their poll results: http://tmsnrt.rs/1QHZulM)