The US electorate is split roughly into 1/3 Republican, 1/3 Democrat, and 1/3 independent. Trump is popular among, at most, 30% of Republicans, 30% of independents and 0% of Democrats. That equates to roughly 20% of voters. The other 80% despise the guy. Even the Koch brothers hate him.

Trump has only been able to make a big noise because the Republican field has been so large that a 30% share is huge compared to that of any other single candidate. As more people drop out of the race and support of the other 70% of Republican and independent voters consolidates behind one or two "mainstream" candidates, Trump will be left far behind.

That doesn't mean Trump's going to go away. He is extremely wealthy and his campaign is self-financed. He doesn't have financial backers to withdraw their support as his poll numbers begin to decrease. He'll just keep throwing his own money at the campaign until he gets tired of playing the game, takes his ball and goes home.