Trump, a billionaire businessman, draws the support of 30 percent of Republican primary voters, while Cruz, a U.S. senator from Texas, draws at 27 percent. Ohio Gov. John Kasich has risen to 22 percent in the survey, while Florida U.S. Sen. Marco Rubio receives 20 percent.
The survey reflects a slight gain from last month for Trump, who in the February survey trailed Cruz by a 28 percent to 26 percent margin. Trump subsequently scored significant victories in South Carolina, Nevada and in several Southern states on Super Tuesday.
The telephone survey of 397 Republican primary voters was conducted March 3 to 6. It carries a margin for error of 4.9 percentage points.
Trump enjoys a far larger margin over Cruz — 39 percent to 20 percent — in the separate NBC/SurveyMonkey online tracking poll, conducted Feb. 29 to March 6. State polls have shown him leading heading into Tuesday night's primaries in Michigan and Mississippi, where Trump hopes to widen his delegate lead.
The former first lady and secretary of state draws support from 53 percent of Democratic primary voters, while Sanders, a U.S. senator from Vermont, draws 44 percent. That's down slightly from her 53 percent to 42 percent edge in last month's NBC/WSJ poll, even though Clinton has gained momentum from her big primary wins on Super Tuesday.
Yet as in the Republican race, the Democratic front-runner holds a larger edge in the NBC/SurveyMonkey online poll. That survey shows her leading Sanders by 55 percent to 38 percent heading into primaries Tuesday night in Michigan and Mississippi. State polls have shown her leading in both states.
The NBC/WSJ poll of 410 Democratic primary voters carries a margin for error of 4.8 percentage points.