There is an uncanny symmetry in the two presidential candidates’ choice of vice presidential running mates – Republican J.D. Vance and Democrat Tim Walz.

They go beyond the fact of their military service. Both were chosen by principals in moments of exuberance: former President Donald Trump after he’d walloped President Joe Biden in debate and survived an assassination attempt, Vice President Kamala Harris after she’d outperformed expectations and surged to a lead in the polls.

Each might have reflected that poll leads can vanish and that, in any case, theirs were not so impressive. Trump never quite reached 50% against Biden, and Harris’ numbers remain well short of Biden’s 4.5-percentage-point popular vote lead that enabled him to win an Electoral College majority by only 42,918 votes in three states.

As it often does with politicians, optimism prevailed. Each nominee — Harris has been nominated preconvention over the internet — chose a candidate whose record accentuated the ticket’s differences from earlier party traditions — and who has seemed less likely than possible alternatives to appeal to voters dismayed by both alternatives.

Vance is a convert, from a 2016 scoffer at Trumpism to a true believer, in a demotic Republican Party that reflects the cultural discontents and economic grievances of a working-class majority — “demotic” comes from the same Greek root as “democracy.” He articulately defends tariffs, scoffs at Ukraine aid, and celebrates family values not just abstractly but with provocative references to “childless cat ladies.”

Walz, despite his roots in Blue Earth County, Minnesota, and occasional centrist congressional votes, has come to represent a metropolitan Democratic Party, whose big majorities in million-plus metro areas owe less to race-defined minorities and more to white college graduates in each electoral cycle.He was sympathetic to rioters in May 2020 — he hesitated before sending in the National Guard. He has called for a “working ceasefire” in Gaza and signed a bill putting menstrual pads in fourth- to 12th-grade boys bathrooms.

The Vance and Walz selections can be explained as attempts to set the course of the parties over the long-term future — a demotic Republican Party that will outlast the 78-year-old Trump, a metropolitan Democratic Party that will expand Harris’ coastal California base to the flyover territories.

But in the short term, the Vance and Walz picks increase the chances the other party will achieve the trifecta — majorities in both houses of Congress and the White House — which both parties have plausibly sought in every presidential year this century. Democrats achieved it in 2008 and 2020, Republicans in 2004 and 2016.

Their 2022 election results suggest that neither vice presidential candidate’s electoral performance adds anything to each party’s appeal.

Vance won his Senate seat in Ohio with 53% of the vote, exactly the same as Trump’s percentage there in 2020. His percentages in metro Cleveland-Akron, 43%, and Columbus, 45%, were identical to Trump’s. He ran 1 point better, 54%, in metro Cincinnati, which includes his boyhood home of Middletown.

In the rest of the state, which includes the smaller Dayton, Toledo and Youngstown metro areas and cast 43% of statewide votes, Vance’s percentage, 62%, was identical to Trump’s.

Walz’s boosters make much of his 2006-16 wins in a mostly non-million-plus metropolitan congressional district, although one reason was his success in Olmsted County, the upscale high-education home of the Mayo Clinic. Statewide, in races for governor, his percentage actually dropped from 54% in 2018 to 52% in 2022. That drop was greatest in the 38% of the state outside metro Minneapolis-St. Paul, from 46% to 40%.

His 2022 performance was uncannily similar to Biden’s in 2020. Both won 52% statewide, both won 71% in the two counties that include metro MSP’s two central cities, and both just narrowly lost, with 48%, in the ring of metro MSP counties beyond. In the rest of the state, Walz’s 40% was just below Biden’s 41%.

These numbers suggest we continue to live in an era of straight-ticket voting, with a close balance between the two parties, as they have come to be defined — and reinforced by the Vance and Walz selections.

Republicans’ hopes of achieving a trifecta appear better than Democrats’ — but far from assured.