Here's a terrible sign for anti-Trump forces: a Carson dropout would make things even better for Trump

Nevada's voters just blew up the best argument for why Donald Trump could still be prevented from winning the nomination.

This argument — that an unusually crowded field hid the true number of "anti-Trump" votes — is incompatible with the massive 46 points the billionaire received on Tuesday night. It just no longer makes that much sense to feel certain that an anti-Trump bloc will consolidate behind the last remaining challenger and expose Trump as a fringe figure.

But the situation gets even worse for party elites when you consider that Marco Rubio — the establishment's last best hope — may actually be doing worse than his second-place finish last night suggests. And that's because the crowded field may now be overestimating Rubio's popularity just as much as, or more than, it is for Trump.

Why the "winnowing" would have hurt Rubio in Nevada

In Nevada, following Trump with 46 points came Rubio with 24, Ted Cruz with 21, Ben Carson with 5, and John Kasich with 3.6.

In previous primaries won by Trump, most observers looked at the vote totals, added up the non-Trump votes, and assumed that Rubio could consolidate the rest of the field and take first place once everyone else left the stage.

But let's say Carson got out of the race tomorrow. Those votes would not go to Rubio. MSNBC's "second choice" polling indicates that Carson voters' second choice is Cruz, who 24 percent would support if Carson dropped out, followed by Trump, who 22 percent would support if Carson exited the race.

So there's an argument that it's Rubio, not Trump, who is now being artificially helped by the crowded field. With Carson out of the race, Rubio would likely have finished third place behind Cruz.

Kasich's paltry 3.6 points in Nevada probably would have gone mostly to Rubio. But that certainly wouldn't have been nearly enough to catch Trump, especially if you include Carson's voters.

The picture looks a little more complicated when you consider national polling. Kasich is polling around 10 points and Carson around 7 points, according to the RealClearPolitics polling average. If you imagine their votes being dispersed among the top three candidates, Rubio might get a small boost. Still, the effect certainly wouldn't be enough to have Rubio catch Trump.

All of that points to the need for Cruz or Rubio to really get out of the race soon for there to be any hope of stopping Trump. But Cruz has no reason to drop out as long as he's leading Rubio in delegates, and Rubio almost certainly won't drop until he's had a chance to run in his home state of Florida on March 15.