I find this train of thought puzzling. Trump is in first place. Why would he switch? He is poised to go all the way.
Fair question.
IIRC, Trump has about 24% of the polling. He knows what some of the GOP herd does not. We conservatives absolutely do NOT want amnesty for illegal aliens (including deceptive titles like "dream" and "pathway" and etc.)
Trump, with all his name recognition and all of his grating bombast, projects an anti-amnesty stance that is heard above all other voices. For now.
As the GOP herd thins, primarywise, and as the pro-amnesty-types like Rubio and Jeb are cast aside by voters like so much stinky trash, the strong and responsible voices will be heard, and Trump will sink, relative to the remaining contenders. And I predict Trump will then start with the Perot-mini-me third party stuff, and I suspect that he has planned to do so all along.