It is recognized by pundits and psephologists that, over time, the most accurate method available of determining a candidates polling is in the aggregate.
This is where all polls are combined for a state or nationally, and by doing so over time the outliers and the most accurate polls merge in to a picture which has, most notably in the 2008 and 2012 presidential elections, been the most accurate.
Both Real Clear Politics and the Huffington Post Pollster use this method. Huffington Post uses every available poll whereas RCP selects polls which, in their opinion, are more accurate and have been in the field for some years.
The Huffington Post poll aggregate for Donald Trump nationwide has been running about 1-2 points higher for him than RCP's but the difference is minimal
If we use the Real Clear Politics aggregate polls
for the states that voted Tuesday March 15th the results were astoundingly accurate for Donald Trump who out performed the aggregate average in every state except one where he was behind by only 1.2 points
The final Ohio aggregate was 35.4% Trump actual was 35.6%
Florida aggregate was 43.0% actual 45.7%
Illinois 36.0% aggregate actual 38.8%
NC aggregate 41.3% actual 40.2% hardly an "under perform"
The only March Missouri poll had Trump at 36% he got 40.9%
Also his national aggregate was 36.0% he averaged around 40% Tuesday
