Marco Rubio took to the ballroom stage two weeks ago in Pittsburgh's Omni William Penn Hotel, the robber baron-era grande dame that has hosted every U.S. president since Teddy Roosevelt.

Rubio's pitch was better than flawless. It was natural, genuine; it so captivated the audience that a pin could have dropped in the room and everyone would have flinched at the annoyance.

In the gilded ballroom sat Western Pennsylvania business people, elected officials, Republican activists and a healthy number of young people not usually found at such events – a changing guard mingling with the establishment to hear the freshman Florida senator's pitch to be the GOP's presidential nominee.

Even the hotel staff paused and watched from the balcony. It was the largest audience in the history of the state Republicans' annual fundraising event — and this in a state whose presidential primary rarely matters because of its late-spring timing.

Rubio effectively persuaded the across-the-board mix of conservatives, even as the political class eagerly proclaimed that entertainer Donald Trump has a lock on the nomination.

Optics aren't everything in American politics but they sure are a big part of winning over persuadable voters and skeptics. Rubio owned the visual part of the winnowing process for voter support in Western Pennsylvania, and again hours later at an event near Youngstown, Ohio.

We are talking rust-belt America here and in two of the three other must-win states needed to capture the presidency. (The third is Rubio's home state, Florida.)

Historically, our presidential primaries are a revolving door of frontrunners; typically, their sustainability depends on how well they handle scrutiny by the press and voters.

This race is no different, with the exception that it is occurring in the midst of a populist wave, a phenomenon that usually falls during a midterm rather than a presidential year. So the energy, optics and scrutiny are louder, more volatile — but the process remains intact.

In short, we will give each candidate their moment in the sun, which might be longer or shorter depending on the individual, but the scrutiny remains the barometer by which Republicans will choose their nominee.

And despite what many say, this race is no lock for anyone. It is fluid, nimble, energetic and curious, all of the things you want when determining your party's nominee.

This populist streak running through the electorate is so misunderstood. First and foremost, it is not the tea-party movement that ended before the last presidential election cycle.

Oh, disruptive voters and candidates are given that label by analysts lacking the intellectual capacity to dig deep or to understand history and political movements. And the “pay for purity” hucksters try to keep it alive and prey on voters' fears, so they can make money or become cable-famous with groups whose names include “Patriot,” “Tea Party,” “Freedom” or “Liberty.”

This populist streak began in 2013, its power and effect built without much notice; it was focused on economic freedom and electing people who would get things done — the “doers” of the world – rather than the tea party's strict ideology.

Just go through the list of 2014's winners: You'll see the evidence in the economics professor who upended former House Majority Leader Eric Cantor and the string of big Senate wins in Colorado, Arkansas, West Virginia, Iowa.

If you understood 2014, you will understand this primary process — but if you thought Kansas would really go Democrat, or Texas' John Cornyn would lose his Senate seat, or Mitch McConnell would lose in the primary or general elections of 2014, then you won't.

Rubio, Sen. Ted Cruz of Texas, New Jersey Gov. Chris Christie and businesswoman Carly Fiorina still are very much part of this primary process.

The question should never have been, “Can anyone stop Donald Trump?” It always should have been, “Do you understand the intelligence, needs and wherewithal of the Republican electorate?” — the real electorate, not the fringy people who bleed talk-radio script and devour social-media spats.

The truth of this year's cycle always has been that any candidate can tap the Republican base's energy next year.

The other truth is that everyone seems to have misread that.

Salena Zito is a Pittsburgh Tribune-Review editorial page columnist. E-mail her at szito@tribweb.com