LAS VEGAS/COLUMBIA, S.C., Feb 20 -- Republican presidential candidate Donald Trump rolled to victory on Saturday in South Carolina in a contest that saw former Florida Governor Jeb Bush drop out, while Democratic hopeful Hillary Clinton beat back a strong challenge from Bernie Sanders in Nevada.

The victories by Trump and Clinton solidified their positions as the front-runners to win their parties' respective presidential nominations ahead of the Nov. 8 election.

Bush suffered a distant fourth place finish in the Republican contest and announced he had suspended his campaign, ending his dream of becoming a third Bush president after his father and brother.

"The people of Iowa, New Hampshire and South Carolina have spoken, and I really respect their decision," an emotional Bush said in Columbia. He finished far out of the running in each of the first three states.

By winning both South Carolina and New Hampshire and holding leads in the 11 states that vote on March 1, Trump was arguably on track to win the nomination, an outcome that seemed astounding to contemplate when he got into the race last summer.

"It's going to be very difficult for him to be derailed at this point," said Hogan Gidley, who was a senior adviser to former Republican candidate Mike Huckabee.

Trump, 69, was declared the victor about an hour after polls closed in South Carolina.

"Let's put this thing away," Trump said in his victory speech in Spartanburg.

Trump was as feisty and anti-establishment as ever, denouncing TV pundits for saying that if his remaining opponents consolidated around one Trump alternative, there would be enough anti-Trump votes to beat him.

"These geniuses," he said. "They don't understand that as people drop out, I'm going to get a lot of those votes also. You don't just add them together."

He easily defeated Florida Senator Marco Rubio and Texas Senator Ted Cruz, who were in a close fight for second place and the right to declare themselves the anti-Trump alternative.

With 73 percent of South Carolina precincts reporting, Trump had 33.1 percent, followed by Rubio with 22.3 percent and Cruz with 21.7 percent.

It was Trump's second victory in a row, an outcome that frightens establishment Republicans but thrills the "throw-the-bums-out" conservative base of the party that has long been fed up with Washington.

The bellicose New York billionaire had created some last-minute drama in South Carolina after Pope Francis said on Thursday his views on U.S. immigration were "not Christian." Trump initially called Francis "disgraceful," but later called him "a wonderful guy."

Trump, who has also advocated a ban on Muslim immigrants to counter domestic terror threats, stirred fresh controversy on Friday when he told a crowd about a U.S. general who was said to have dipped bullets in pigs' blood to kill Muslim prisoners a century ago.

After South Carolina, the Republican presidential campaign is about to rapidly pick up steam in March when dozens of states hold nominating contests. Another candidate, Ohio Governor John Kasich, is concentrating on midwestern and northern states in the state-by-state contest to pick nominees for the Nov. 8 election.

Clinton's victory in the Nevada Democratic caucuses, meanwhile, could help calm Democratic Party worries about the strength of her campaign.

Her win denied Sanders the breakthrough win he had sought in a state with a heavy minority population, but his ability to close a one-time double-digit polling lead for Clinton suggests the Democratic nominating race will be long and hard fought.

With 87 percent of precincts reporting, Clinton was leading with 52.5 percent of the vote to Sanders' 47.4 percent. Vote counting was delayed in Nevada by heavy turnout.

Clinton's victory buoyed worried supporters and gave her fresh momentum as she heads into the next contest in South Carolina on Feb. 27, where polls show her with a double-digit lead largely as a result of heavy support from black voters.

"Some may have doubted us, but we never doubted each other," she told cheering supporters at a victory rally in Las Vegas. "This is your campaign."

Sanders vowed to fight on and set his sights on the 11 states that vote on "Super Tuesday," March 1. He predicted that when Democrats gather for their nominating convention in Philadelphia in July, "We are going to see the results of one of the great political upsets in the history of the United States."

"The wind is at our banks," he said. "We have the momentum."

After routing Clinton in New Hampshire and finishing a strong second in Iowa, states with nearly all-white populations, Sanders had hoped to prove in Nevada that he could win over black and Hispanic voters and compete nationally as the race moves to states with more diverse populations.

But entrance polling in Nevada showed he badly lost among black voters, by 76 percent to 22 percent, a bad omen for South Carolina and other southern states with big black populations. He did win among Hispanics by 53 percent to 45 percent.

Clinton's campaign has argued she would assert control of the Democratic race once it moved to more diverse states with black and Hispanic populations who have traditionally backed Clinton and have been slow to warm to Sanders.