From article (curious weighting):
Another possible explanation for Trump’s decline in the new NBC/WSJ poll is an increase in “very conservative” Republican voters from January’s sample.
If the current poll is re-weighted to reflect the ideological composition from last month, the GOP horserace numbers are: Trump 26 percent, Cruz 25 percent, Rubio 18 percent and Kasich 13 percent — so Trump is ahead by one point, but still down from January.
I wonder what else was changed besides the weighting to a more very conservative polling sample? This could be a shift or an outlier poll. We will know Saturday.