Poll: Cruz within 3 points of Trump nationally
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Trump has 30 percent support, according to the NBC News/Wall Street Journal survey, with Cruz at 27 percent.
Last month's version of the same poll found Cruz two points ahead of Trump. It was the only poll since November to show someone other than Trump leading the field nationally.
Tuesday's results show a tightening in the GOP field overall, with 10 points separating all GOP candidates.
Kasich's support is double the 11 percent he got in last month's version of the poll.
The NBC/Journal poll also found Trump losing in hypothetical head-to-head match-ups with his GOP rivals.
Cruz and Kasich each best Trump, 57 to 40 percent, while Rubio tops Trump by slightly less, 56 to 43 percent.
A separate national survey from ABC News and The Washington Post released earlier Tuesday found Trump losing in head-to-head match-ups with Cruz and Rubio. A head-to-head with Kasich was not measured.
The polls come as Republicans are battling in four contests Tuesday: Michigan, Mississippi, Idaho and Hawaii. 
The NBC/Wall Street Journal national poll of 397 GOP primary voters was conducted March 3-6 via landlines and cellphones, with a margin of error of 4.9 percentage points.