The American presidential nominating process is a grueling exercise.

It’s also a useful one.

The Iowa caucuses are about to begin in three weeks. Right after we’ll witness the New Hampshire primary elections.

The usefulness comes in the form of the culling of the fields that’s about to commence.

The candidates at the back of the Republican and Democratic packs have been able to retain their campaign viability by insisting that “no votes have been cast.” That argument ends in Iowa.

Who’ll pack it in?

Martin O’Malley will exit the Democratic Party race, leaving the field to just Hillary Rodham Clinton and Bernie Sanders.

On the Republican side, the outcome is a bit murkier.

It has become a battle for third place. The top two spots will go to Ted Cruz and Donald Trump. Third? It’ll be either Marco Rubio, Chris Christie or maybe Jeb Bush. After that, the rest of ’em ought to bail out.

Rick Santorum, Mike Huckabee, Ben Carson, Carly Fiorina, John Kasich, Rand Paul and Jim Gilmore (yes, the former Virginia governor’s still in the hunt) all need to exit the stage.

Of the also-rans, my biggest disappointment would be Ohio Gov. Kasich. He’s got a tremendous substantive argument to make: that he, as House Budget Committee chairman in the late 1990s, helped produce a balanced federal budget by working with President Bill Clinton.

That hasn’t worked with the GOP base, which lusts for the red meat being fed to it by the likes of Trump and Cruz.

The process, though, does produce winners. It’s often not pretty to watch. This year has been ugly, to be sure.

However, the process has worked every four years for as long as most of us can remember.

The serious winnowing of both parties’ fields will commence soon.

Let’s all stay tuned.