(CNN) Donald Trump and Hillary Clinton are poised to lead the nation's two major parties in this fall's presidential election, with a new nationwide CNN/ORC poll finding each well ahead of their closest competitors just as the race expands to a national stage.

Trump has expanded his lead over the diminished field to capture the support of nearly half of Republican voters, while Clinton tops Sanders by nearly 20 points.

On the Republican side, the new survey finds Trump's lead is dominant, and his support tops that of his four remaining opponents combined. The businessman tops his nearest competitor by more than 30 points: 49% back Trump, 16% Marco Rubio, 15% Ted Cruz, 10% Ben Carson and 6% John Kasich.

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Trump's supporters are incredibly enthusiastic about the coming election, and largely committed in their support for him. Nearly 8 in 10 say that they are more enthusiastic about voting this year than in previous elections, among Republicans who are not supporting Trump, just 39% say they are more enthusiastic than in years past. Likewise, 78% of Trump's backers say they will definitely support him vs. 22% who say they could still change their minds. Among those backing other candidates, 57% say they are committed to their chosen candidate.

The survey asked those Republicans not currently backing Trump whether they would support him if he became the party's nominee, and just a quarter of Republicans overall say they probably or definitely wouldn't support him in November. That's about the same as the share saying they wouldn't back Rubio or Cruz.

Photos: Who's running for president? Ted Cruz, Donald Trump, John Kasich, Hillary Clinton and Bernie Sanders, Hide Caption 1 of 6 Photos: Who's running for president?



"So, ladies and gentlemen, I am officially running for president of the United States, and we are going to make our country great again," Trump told the crowd at his announcement. Businessman Donald Trump announced June 16 at his Trump Tower in New York City that he is seeking the Republican presidential nomination. This ends more than two decades of flirting with the idea of running for the White House."So, ladies and gentlemen, I am officially running for president of the United States, and we are going to make our country great again," Trump told the crowd at his announcement. Hide Caption 2 of 6 Photos: Who's running for president?



"These are all of our stories," Cruz told the audience at Liberty University in Virginia. "These are who we are as Americans. And yet for so many Americans, the promise of America seems more and more distant." Sen. Ted Cruz of Texas has made a name for himself in the Senate, solidifying his brand as a conservative firebrand willing to take on the GOP's establishment. He announced he was seeking the Republican presidential nomination in a speech on March 23."These are all of our stories," Cruz told the audience at Liberty University in Virginia. "These are who we are as Americans. And yet for so many Americans, the promise of America seems more and more distant." Hide Caption 3 of 6 Photos: Who's running for president? Ohio Gov. John Kasich joined the Republican field July 21 as he formally announced his White House bid.



"I am here to ask you for your prayers, for your support ... because I have decided to run for president of the United States," Kasich told his kickoff rally at the Ohio State University. Hide Caption 4 of 6 Photos: Who's running for president?



"Everyday Americans need a champion, and I want to be that champion -- so you can do more than just get by -- you can get ahead. And stay ahead," she said in her announcement video. "Because when families are strong, America is strong. So I'm hitting the road to earn your vote, because it's your time. And I hope you'll join me on this journey." Hillary Clinton launched her presidential bid on April 12 through a video message on social media. The former first lady, senator and secretary of state is considered the front-runner among possible Democratic candidates."Everyday Americans need a champion, and I want to be that champion -- so you can do more than just get by -- you can get ahead. And stay ahead," she said in her announcement video. "Because when families are strong, America is strong. So I'm hitting the road to earn your vote, because it's your time. And I hope you'll join me on this journey." Hide Caption 5 of 6 Photos: Who's running for president?



"This great nation and its government belong to all of the people and not to a handful of billionaires, their super PACs and their lobbyists," Sanders said at a rally in Vermont on May 26. Sen. Bernie Sanders , an independent from Vermont who caucuses with Democrats, announced his run in an email to supporters on April 30. He has said the United States needs a "political revolution" of working-class Americans to take back control of the government from billionaires."This great nation and its government belong to all of the people and not to a handful of billionaires, their super PACs and their lobbyists," Sanders said at a rally in Vermont on May 26. Hide Caption 6 of 6

Trump is widely viewed as the candidate in the field who would be most effective at solving the country's problems, 51% vs. 17% for Cruz, 13% for Rubio and 10% for Carson, and as being best able to handle the responsibilities of being commander-in-chief, 48% say so, compared with 17% for Cruz and 15% for Rubio. The billionaire is also seen as the one who best understands the problems facing people like you, 46% Trump vs. 18% Cruz and 15% Rubio.

As accusations of dishonesty have flown between Trump, Cruz and Rubio, voters say they are more apt to see Trump as honest and trustworthy. Asked who of the five candidates is most honest and trustworthy, 35% name Trump, 22% Carson -- who has largely stayed out of the mudslinging - 14% Cruz and 13% Rubio.

On the Democratic side, Hillary Clinton tops Bernie Sanders 55% to 38% in the new poll, a slightly wider margin than she held in late January before any primaries or caucuses were held.

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There are sharper demographic splits among the Democratic electorate than on the Republican side. Men, younger voters, independents and liberals are all about evenly split between Clinton and Sanders, while Clinton's lead rests on large advantages among women, older voters, Democrats and moderates.

Democrats are more apt than Republicans to say they would support either of the remaining top candidates should they become the nominee. Just 15% each say they wouldn't back Clinton or Sanders.

Clinton tops Sanders handily as the candidate who would be more effective at solving the country's problems and can better handle the responsibilities of being commander-in-chief, but Sanders fares better than Clinton on honesty, 59% say he is more honest and trustworthy vs. 36% who say Clinton is. Overall, voters are split on whether Clinton or Sanders better understands the problems facing people like you, 49% say Clinton, 48% Sanders.

The CNN/ORC Poll was conducted by telephone February 24-27 among a random national sample of 1,001 adults. Results for the 418 registered voters who are Democrats and Democratic-leaning independents have a margin of sampling error of plus or minus 5 percentage points. It is the same for results among the 427 Republican and Republican-leaning voters.