One important stat I haven't seen reported is each candidate's share of the delegates that have been awarded so far. Ultimately the nominee needs 50% of all delegates, but let's just check on how they're doing with those awarded up through Super Tuesday.
Name, % of popular vote, % of delegate pool
Trump__ 34, 46
Cruz____ 28, 32
Rubio___ 22, 16
Kasich__ 07, 04
The only one close to achieving 50% is Trump, and he's more or less there already. All he needs is to keep or improve on that share, while racking up the absolute number in race after race.
Really the only thing keeping him under 50% right now is the large influence of Texas, which will not be representative in the future. There are no more Plains / Mountain states with anywhere near 155 delegates, where Cruz can clean up while Trump takes little away.
In fact, if we look at all states except Texas, Trump is a few points over 50% in the delegate share. That also means that Cruz's share is going to start dipping down toward 20-25%, while Rubio's share will also rise toward 20% or so as we move northward. Kasich won't budge much.
It's not hard to imagine Trump getting 55%, Cruz and Rubio 20% each, and Kasich 5%, when all's said and done. Assuming that all four stay in the race all the way through.
Note also that Trump has leveraged his popular vote share into an even higher share of the delegates -- so much for the idea that he can't win the nomination with "only" 35-40% of the popular vote. Once the winner-take-all states come into play, he'll leverage even further, like he did in South Carolina. No more micro-cuts bleeding his delegate count from the also-rans getting their proportional share.
By contrast, Cruz, Rubio, and Kasich will all be under-performing in the delegate share based on their share of the popular vote. Haw haw.
Don't worry too much about how close he is to the finish line -- he's 27% of the way there, which doesn't sound like too much. But when you look at his share of the delegates, it was over 60% after South Carolina and after Nevada, it was over 50% after Super Tuesday except for Texas, and is at "only" 46% including Texas. That will only improve going forward.
It looks to only be a matter of time before "50% of delegates so far" becomes "50% of all delegates," and he's the nominee.
All this continued talk about a brokered convention is turning out to be pure fantasy. Depending on whether everyone else stays in the race, he could wind up getting a comfortable 55-65% of all delegates, and leave no room for doubt.