In recent weeks, the Republican presidential race has focused quite naturally on poll leader Donald Trump — the mere mention of whom drives extensive Internet traffic — and his fellow outsider hopefuls, Dr. Ben Carson and Carly Fiorina.

But just below the surface, four candidates polling mostly in the single digits are jockeying to represent the GOP’s establishment wing in what many analysts believe will ultimately be a showdown with Trump or perhaps one of the others.

Presumably, the battle among former Florida Gov. Jeb Bush, New Jersey Gov. Chris Christie, Ohio Gov. John Kasich and Florida Sen. Marco Rubio won’t sort out until the voters in Iowa, New Hampshire, South Carolina and Nevada vote next February. Before then will be four more GOP televised debates, climaxing in a mid-January confrontation in Iowa.

But since the Sept. 16 debate, there are signs Rubio is emerging as the strongest of the four — hardly surprising to many observers, especially Democrats who long have feared his combination of youth, Hispanic background and Florida residence made him the most potentially potent GOP challenger.

Explaining attacks on Rubio from both outsider and establishment rivals, Politico’s Glenn Thrush said, “No other candidate poses such a threat to either flank, so he should take it as a compliment.”

He cited the 44-year-old’s unique combination of youth, political talent, a plan to win, a record sufficiently conservative for most Republicans and a history of having “always outperformed expectations,” starting with his 2010 election to the Senate.

His seat on the Senate Foreign Relations Committee lets him speak with more authority on foreign policy than governors, and his four years as speaker of Florida’s House gives him management experience senatorial rivals lack.

Like all other candidates in both parties, he has handicaps. He angered some conservatives by helping Senate Democrats pass a compromise immigration bill (which he has since renounced), and he so far lacks enough strength in the early states for a necessary breakthrough, though South Carolina’s hawkishness and Nevada’s substantial Hispanic population might provide that.

Still, his main establishment hopefuls have all encountered difficulty, raising doubts they top both Trump and Rubio when the race reaches its crucial stretch.

Bush started as the clear favorite for establishment support, based on his ability to raise money, his family’s history of success and his Florida record, but his poll numbers have steadily dropped amid considerable anecdotal signs Republicans are cool to nominating another Bush.

He has suffered from the kind of inarticulate explanations that pass for “goofs” in today’s over-heated political media world. That includes last week’s reaction to the Oregon shootings: “Stuff happens” that doesn’t always require a governmental response. Such moments might reflect the rustiness of someone who hadn’t sought office in 14 years.

Kasich has performed well in New Hampshire, home of the first primary, by spending a great deal of time and money there and presenting himself as a sensible conservative like others who have done well there in recent years. But he trails badly both nationally and in the first caucus state of Iowa, whose results often influence New Hampshire’s voting just eight days later.

His views are only marginally different from many other hopefuls: He opposed a government shutdown, though he favors defunding Planned Parenthood; he enabled Ohio to participate in the Medicaid expansion through Obamacare; and he favors legal status for undocumented immigrants. He has stressed his governmental experience in a year many Republicans consider that a detriment.

Christie has never overcome the negative impact of the highly publicized incident in which top aides stopped George Washington Bridge traffic to punish the Democratic mayor of Fort Lee. He performed well in the last debate but has yet to show he can gain necessary traction in New Hampshire.

For some time, Rubio has shown the potential to become the Republican Hispanic Obama, a historic figure who could reverse recent GOP setbacks with Latinos. But questions remain about whether his Cuban background will appeal to the predominantly Mexican Hispanics in key Western states and whether his youth and personal political skills can surmount his very conservative positions on women’s issues, immigration and foreign policy.

Still, four months before the voting begins, he remains the Republican candidate with the most long-term potential.

— Carl P. Leubsdorf is the former Washington bureau chief of the Dallas Morning News.