Let’s talk geopolitics.

Now that three female senators — Kamala Harris of California, Amy Klobuchar of Minnesota and Elizabeth Warren of Massachusetts — have used deft debate performances to rock the septuagenarian male front-runners off their pedantic pedestals, geography rather than gender is coming into play.

The United States may have a national culture — and television (and then the internet) may have smoothed over geographical differences — but regional identity still matters. Why else would Vernors ginger drink be a beloved Michigan specialty? Why else would coffee milk and frozen lemonade be Rhode Island favorites? Why else would Pittsburghers insist that a jagoff was a noun, and that it isn’t offensive? And come to think of it, why do some people call it a submarine sandwich and others call it a grinder, or a hoagie, or simply call it an Italian?

Politics is no different. The Electoral College is not the only place where national preferences and choices are trumped by regional factors. So, too, is the process that leads to a presidential nomination — which is why Mses. Harris, Klobuchar and Warren are on the verge of transforming strong national debate performances into powerful geographical advantages, with important consequences.

Ms. Klobuchar and Ms. Warren are from states that share borders with vital early political states, and Ms. Harris was elected to two major offices in a state that votes early in the nomination process and that delivered a 62 percent margin of victory to former Secretary of State Hillary Rodham Clinton three years ago — 2 percentage points above the customary political definition of a landslide. Ms. Clinton did far better in California than Donald J. Trump did in Mississippi.

Ms. Klobuchar’s Minnesota shares a border with Iowa, where the precinct caucuses are the first political test of the 2020 presidential election. (Iowa is surrounded by six states; and in the first caucuses, in 1972, three of the four contestants in an inconsequential contest, conducted before the caucuses were freighted with their contemporary meaning, actually were from neighboring states.)

Over the years, candidates from Iowa’s neighbors have found the Hawkeye State to be a peculiarly congenial battleground. Minnesota’s Walter F. Mondale won the state in 1984, and Missouri’s Richard A. Gephardt won four years later, with Illinois’ Paul Simon taking a strong second place. All three profited from the advantage Ms. Klobuchar is prepared to weaponize: busing scores of supporters to flood meaningless but highly visible events like the steak fry scheduled for Sept. 21 in the Water Works Park in Des Moines. Already 20 of the candidates have confirmed they will be there.

Now to Ms. Warren and the New Hampshire advantage. It is true that Sen. Edward M. Kennedy of neighboring Massachusetts did not prevail in the 1980 contest, but he was running against an incumbent president, Jimmy Carter. It is true that former Gov. Mitt Romney did not win in 2008, but he was running against Sen. John McCain of Arizona, who had won the contest in 2000 and campaigned like an incumbent. (Mr. Romney recovered and won the primary in 2012.)

But consider the success Granite State neighbors have had over the years. Sen. Bernie Sanders of Vermont won the primary in 2016. Massachusetts winners, besides Mr. Romney’s second-chance triumph, include Democrats Sen. John F. Kennedy (1960), Gov. Michael S. Dukakis (1988) and Sen. John F. Kerry (2004), and the Republican write-in candidate, Ambassador Henry Cabot Lodge (1964). Many people believe Gov. Bill Clinton of Arkansas won the contest in 1992, but the winner was former Sen. Paul E. Tsongas of Massachusetts. And while the folklore says that Sen. Edmund S. Muskie of neighboring Maine lost New Hampshire in 1972, he actually won — but his margin over McGovern was so small he was damaged by his victory.

Now New Hampshire looms as the unlikely staging ground for a dramatic struggle between two stern New England neighbors, Mr. Warren and Ms. Sanders, progressive titans with the most developed policies in the field. The two have cadres of home-state supporters who can flood over the southern and western borders of New Hampshire to provide canvassing armies, phone bank legions and get-out-the-vote couriers.

There never has been a “home game” struggle quite like this in New Hampshire, which within living memory was so conservative that its governor, Meldrim Thomson Jr. (in office 1973-1979), put the state on record for American withdrawal from the United Nations and also advocated arming the state’s National Guard with nuclear weapons. Slightly earlier, Sen. Styles Bridges (governor 1935-1937, senator 1937-1961) was regarded as the reactionary’s reactionary and voted against condemning Sen. Joseph R. McCarthy.

The big winner of the debates and the calendar may be Ms. Harris, who opened her campaign with astonishing fanfare, then slipped from view, and finally surged to new prominence after challenging the civil rights record of former Vice President Joseph R. Biden, who as a onetime Delaware senator and a Scranton neighbor has been counting on a strong performance in Pennsylvania’s primary, which to his disadvantage is late in the process — April 28.

That is eight weeks — a lifetime in politics! — after the California primary, moved from its customary early-June slot to March 3. In her 2016 Senate campaign, Ms. Harris prevailed with 62 percent of the vote, another landslide. She has to be regarded as the prohibitive favorite in California, which will account for more than a quarter of the delegates required for the Democratic nomination.

Ms. Harris won’t get all those delegates, of course, and she’s not the only Californian in the race. Rep. Eric M. Swalwell Jr., with a base in Alameda and Contra Costa counties near San Francisco, is also a presidential candidate with a breakout moment in the Miami debate.

He recalled that Mr. Biden, who would be 81 years old when his first term drew to a close, once called upon his elders to pass the torch to a new generation of leaders, and he challenged Mr. Biden to pass the torch himself. A moderator asked: “Vice president, would you like to sing a torch song?” But it was more a night to be torched than to sing.

Indeed, perhaps the song being sung is a farewell — to the notion that biology is destiny. Perhaps the new ballot ballad is a hello — to the idea that geography is destiny.

Swalwell has since dropped out of the race.

David M. Shribman is a former and now emeritus executive editor of the Post-Gazette and a nationally syndicated columnist.