Donald Trump leads Republican field nationally by more than 20 points - Reuters/Ipsos poll

Donald Trump has taken a more than 20-point lead over U.S. Senator Ted Cruz of Texas in the Republican race for the presidential nomination, bolstering his position ahead of the party's primary in South Carolina on Saturday, according to a national Reuters/Ipsos poll.

Among Republicans, Trump, a billionaire businessman, drew 40 percent support in the poll conducted from Saturday to Wednesday, compared with 17 percent for Cruz, 11 percent for U.S. Senator Marco Rubio of Florida, 10 percent for retired neurosurgeon Ben Carson, and 8 percent for former Florida Governor Jeb Bush.

The results contrasted with those of a national poll conducted this week by NBC News and the Wall Street Journal that showed Trump dropping into a national dead heat with Cruz in the race for the Republican nomination for the Nov. 8 election to succeed Democratic President Barack Obama.

On the Democratic side, the Reuters/Ipsos poll showed former Secretary of State Hillary Clinton maintaining about a 10-point national lead over U.S. Senator Bernie Sanders of Vermont since last week's New Hampshire primary won by Sanders.

The Republican results marked an improvement for Trump since his win in the Feb. 9 New Hampshire primary, when he led Cruz by 18.4 points in the national rolling survey, although the increase remained within the poll’s credibility interval.

Since he announced his candidacy last summer, Trump has leveraged his celebrity and deep pockets to wage an unfiltered campaign that has upended the Republican primary. He has led the Reuters/Ipsos daily tracking poll since nearly the start of his campaign, topping Bush in late July.

The Reuters/Ipsos poll also showed that either Clinton or Sanders would win a hypothetical general election contest with Trump. Clinton would likely win with 44 percent support, compared with 37 percent for Trump. Sanders would likely win by 44 percent to 35 percent.

The poll included responses from 476 registered Republicans and 543 registered Democrats. It had a credibility interval of about 5 percent.