Interesting analysis of Donald Trump I found posted elsewhere:
Notice that every time he takes a strong position on something - it's the strongest and the most extreme one he can take without actually getting totally stumped
Deportation of illegals, The Wall, China muslim ban now serve as a few examples.
By comparison his moderate positions are barely ever mentioned even though they are bigger in number.
Why does he do this? Several reasons:
1) To dominate the news cycle - you will be hearing nothing but Trump for the next few days, even more than you normally do.
2) The truthful hyperbole - Trump describes this oxymoron in The Art of the Deal - he has been using it for years - by friendly exxageration you draw the attention to the issue at hand and force others to discuss it, making them realize that there is actually a problem, even if it is not as big as you presented it.
3) To appear as the leader on the issue so he can frame the discussion - the issue of problems of islamic immigration is now firmly in Trump's hands, just 24 hours after Obama delivered just his 3rd, very weak speech from the Oval Office on the same theme. Trump is forcing everyone to react to him and it does not matter than most media and representatives don't support him.
4) To have a strong starting position so he can negotiate down later - Trump won't deport 12 million Mexicans and he won't ban muslims from entering the country. However, he has put himself into a position to accomplish these goals at least partially once he is done negoatiating about them.
5) To lock down his base - not much to explain here even though I think it's only a secondary motive.
Trump is obsessed with deals and has been his whole life. This is the biggest one yet and he is playing by the same rules he has always played by... and he is winning.