Pundits have been declaring for months that Trump was at his ceiling -- 25 percent, then 33 percent. But he kept smashing that ceiling. Today comes a startling CNN poll showing Trump at 49 percent nationally.

If his ceiling is really at 50 percent, then almost nothing could stop him from winning the nomination.

Trump is certainly the heavy favorite to win the nomination, and his "ceiling" has certainly elevated since the fall, but there are many reasons to discount this CNN survey.

The CNN poll's weaknesses

First, it's a nationwide poll. There is no nationwide primary. That limits the poll's usefulness. On the other hand, if the question on the table is Trump's ceiling--and whether he can win the GOP nomination in a two-way race--then this number is interesting. But...

Second, it includes only 427 Republicans, and has a margin of error of plus or minus 5 percent. That is a very small sample size for a national poll and a very large margin of error for a poll that is getting so much attention.

Third, it is a poll of registered voters, not likely voters. Trump does better in registered voter polls -- 4 points higher -- than in likely voter polls, going back to January 21.

Fourth, half of the poll was conducted before the Thursday night debate, when Rubio and Cruz began to hammer Trump.

Still, this is big for Trump

But even if you take away that 4-point unlikely-voter bump for Trump, he's at 45 percent. Even if you then subtracted the entire margin of error (which is an extremely ungenerous thing to do), he's down to 40 percent, and still 20 points ahead of Rubio of Cruz. Almost every other national poll since November shows Trump up double digits.

In short, don't put much stake in this CNN poll. It's a high outlier for Trump, but it's not too far beyond the norm.

Timothy P. Carney, The Washington Examiner's senior political columnist, can be contacted at tcarney@washingtonexaminer.com. His column appears Tuesday and Thursday nights on washingtonexaminer.com.