In political science, 2016 will go down as the election in which the political parties – which used to exercise unchallenged control over the nomination – have seen their control of the process decline to near zero. With the withdrawal of Marco Rubio the GOP field is down to Kasich (who isn't going to win anything other than Ohio), Ted Cruz (who literally everyone hates), and a frontrunner about whom establishment Republicans are literally kept awake at night trying to think of ways to prevent him from winning.
On the Democratic side the party establishment is on the verge of getting exactly what it wants, of course. It is difficult to say whether that is because of the influence of the party or spurious to it; perhaps Bernie Sanders wouldn't have the juice to win the nomination regardless of whether the party supported him explicitly.
At least on the GOP side it is fair to say that the heavy hitters have had no influence on the outcome this year. The Koch Brothers' candidate didn't even make it to Iowa. Sheldon Adelson swung and missed, as did the other big money men who poured money into failing Bush and Rubio campaigns, among others. Republicans with the highest name recognition, people like Paul Ryan, Mitt Romney, and John McCain, have done everything but beg party voters to reject Trump. The RNC has not lifted a finger to assist him but has given considerable support to other campaigns that have failed. The diminution of party influence, which began with the Democratic Party after the debacle of 1968, seems to have crossed the partisan aisle to reach its zenith.