Donald Trump is dominating the GOP presidential field in the first three states to vote in the 2016 campaign, including in Iowa where he has extinguished the lead once held by Sen. Ted Cruz of Texas, a new Wall Street Journal/NBC/Marist Poll finds.

In New Hampshire and South Carolina, Mr. Trump leads by double-digit margins. In all three states he is the first choice of more than 30% of people likely to vote in the Republican primaries or caucuses.

...