Donald Trump has been bragging for weeks now about how he has been bringing new voters into the GOP in order to vote for him. It's what's helped him win many states, and it's what's helped him regain momentum after an embarrassing Saturday. However, in the long run, the strategy is meaningless.
Democrats crossing over to vote for Trump and liberal independents registering to vote for him is not a sustainable general election strategy. While most of the conventional wisdom of the past has flown out the window to escape the insanity of 2016, Democrats will vote for Democrats. Republicans are the ones who are not guaranteed to vote for Republicans.
You need only look at the numbers by which Trump is voting to see this. He, without exception, has been kept under 50% in every state, including Mississippi. A majority of Republicans do not want him and a high percentage of Republicans will refuse to vote for him if he is the nominee. The subtraction of these voters, plus the inevitable subtraction of the liberals voting for him in the primaries, leads to the one certainty virtually every other Republican in the race has said: Trump will not defeat Hillary Clinton. Hell, he can't even beat Bernie Sanders, should that somehow be a thing that happens.
Yet, Trump insists that this new coalition he's built, whether it's liberals participating in their own version of Rush Limbaugh's infamous Operation: Chaos or white supremacists who normally won't vote except when someone appeals to their Final Solutionism, will stick around in the general, as well as the Republicans who have been turning out in record numbers to oppose him. This is plain wrong, and it will cost Republicans the general election.