The national online poll from April 4-8 showed that 42 percent of Republicans support Trump, compared with 32 percent for Cruz and 20 percent for Kasich.
Trump has topped the poll of Republican voters since July, though his lead narrowed considerably in recent weeks as Trump retweeted unflattering pictures of Cruz's wife and his campaign manager was charged with battery in an incident involving a reporter at a campaign event.
Meanwhile, former Secretary of State Hillary Clinton led Senator Bernie Sanders of Vermont for the Democratic nomination. The poll showed that 53 percent of Democrats support Clinton and 43 percent support Sanders.
The poll included 626 Republicans and 668 Democrats and has a credibility interval of 4.6 percentage points.