Is Kamala Harris’s surge beginning to ebb?

That’s the question raised by this morning’s New York Times/Siena College poll, which finds Donald J. Trump narrowly ahead of her among likely voters nationwide, 48 percent to 47 percent.

To me, the result is a bit surprising. It’s the first lead for Mr. Trump in a major nonpartisan national survey in about a month. As a result, it’s worth being at least a little cautious about these findings, as there isn’t much confirmation from other polls.

That said, it wouldn’t be hard to explain if Vice President Harris’s support really has faded a bit in recent weeks. After all, she was benefiting from an ideal news environment: an uninterrupted month of glowing coverage from President Biden’s departure from the race in July to the Democratic convention in August. It’s possible she was riding a political sugar high; if so, it would make sense if she came off those highs in the two uneventful weeks since the convention.

There’s also a plausible reason the Times/Siena poll would be the first to capture a shift back toward Mr. Trump: There simply haven’t been many high-quality surveys fielded since the convention, when Ms. Harris was riding high. There was a scattering of online polls this week, but there hasn’t been a traditional high-quality survey with interviews conducted after Aug. 28.

Why haven’t there been more polls? One explanation is Labor Day weekend, which always puts a pause on polling. It’s also plausible that many pollsters might prefer to wait until after the debate Tuesday before taking another poll. Whatever the explanation, the Times/Siena poll would be one of the first opportunities to pick up a reversion back toward Mr. Trump.