And, reading between the lines of your post, you believe that Trump will do nothing BUT compromise because the man has no core principles. Since he believes in nothing, he will settle for anything.
As to bringing states into the fold, the latest polls in Mississippi and Utah indicate that Hillary is within three points of Trump in those solidly Republican states. So, one has to factor in the states that Trump would LOSE in addition to ones he has a tiny outside chance of bringing in.
And then there's the 75% of women, 81% of Hispanics and 94% of blacks who despise Trump, the vast majority of whom would never vote for him. Then, there's the #NeverTrump group, estimated to be 25% of the GOP electorate.
You are engaged in wishful thinking which has no connection to reality.
Still waiting for you to show some historical data on the accuracy of state polling 7 months prior to an election...guessing I shouldn't hold my breath on that one, right?
Trump will easily hold together all of the current GOP states...as will any of the current GOP candidates in the race. The question is, who can win Ohio, Florida, Virginia, Pennsylvania, Iowa, Colorado, Wisconsin and New Jersey. Current polls mean virtually nothing...horse race polls (Dem vs Repub) are useless this far out (see Reagan way behind Carter in 1980).
What is relevant is enthusiasm, strength with independents (as shown in actual primary vote totals), and positioning on specific issues the public views as most important (Immigration, Economy, Defense, etcetera). On the flip side, issues like religious liberty and abortion may be important to strong Conservatives...but they rate far lower on the scale for Reagan Democrats and right leaning Independents (precisely the people we MUST win over to win). Cruz is so far right, he has no hope of swaying those who are not already in his camp...and as he is entirely unable to compromise, he has no maneuver room to pull from outside his current comfort zone. The GOP nominee must be conservative, as Reagan was, but his appeal must be much broader than a narrow strip of Evangelical voters.
Trump will compromise. If you think that's a bad thing, you fundamentally misunderstand democracy. The point here is, Trump will compromise in a way that ensures he gets 90% of what he and conservatives want...you know, as Reagan did. You can feel free to support the Cruz approach of holding out for 100% of everything Cons want on a particular issue...and achieve nothing but a sense of self satisfaction because you "didn't compromise". That's a horse you can ride into political oblivion...you may enjoy the ride but the end result is nothing.
So continue thinking that any and all compromise is equivalent to surrendering all of your values...if that makes you feel better. In the real world, its more complex than that and a President must be able to persuade AND compromise...the key is how much and how effectively he does both. You can't have a leader who do neither of those things, and that is why Cruz cannot be effective.