Columnist

On Tuesday, Virginia's voters confront what will almost certainly be the most consequential election for governor of their lifetimes.

The contest between Democratic Lt. Gov. Ralph Northam and Republican Ed Gillespie matters for the state, of course, but its implications will be even larger for the nation.

A Northam victory would send a signal to the country that President Trump is a severe drag on the GOP, especially if it were combined with Democratic pickups in the legislature. This would bolster the forces trying to contain Trump's abuses and give heart to those doing the organizing work against him at the grass roots.

It would tell Republicans in Congress that coddling and imitating Trump carry a high cost while strengthening Democratic efforts to recruit strong candidates for the 2018 midterms.

A win by Gillespie would convey exactly the opposite message. It would ratify the Republican candidate's vile and dishonest campaign tying Northam to felons and criminal gangs. This, in turn, would lead to more ugly racial and anti-immigrant appeals by GOP candidates next year. The party would decide that playing around with a few of Trump's more hateful themes was the way to go. The race to the bottom would continue.

[The Post’s endorsements in Virginia]

A Northam defeat would also demoralize Democrats, who up to now have had grounds for believing that anti-Trump sentiment has energized their side. Mobilization is the key, both on Tuesday and in 2018. A mediocre Democratic turnout in Virginia would bode ill for next year.

If Gillespie prevails, Trump will, for all these reasons, be very, very happy. Independents and Democrats who are thinking of staying home should ponder whether they really want to put a big smile on the face of a president who is busily tearing apart political norms and undermining a legitimate investigation into his campaign.

It is commonly said that off-off-year elections such as those in Virginia and New Jersey this week are over-interpreted and over-spun.

Well, sure. Give political pundits a few election returns and they will always squeeze them as hard as they can to extract every drop of deep, long-term meaning. Give political operatives a chance to make sweeping claims on behalf of their respective parties and they'll take it every time.

But guess what? These post- ­presidential races have, in fact, been predictive in the past. Most recently, the big 2009 Republican triumphs in these two states proved to be genuine harbingers of the Democratic catastrophe in 2010.

And the interpretations of this showdown are already baked in. If Democrats lose, they will no doubt try to discount the wider significance of the result by blaming Northam for whatever mistakes he and his campaign made.

It won't work.

This is a state that voted for Hillary Clinton last year. According to the Washington Post-Schar School poll, 59 percent of likely voters disapprove of Trump's performance in office; only 38 percent approve. If Trump doesn't hurt Republicans in Virginia, where will he hurt them?

Along similar lines, Republicans will try to write off a Gillespie loss as inevitable, precisely because of those anti-Trump numbers. But in doing so, they will be conceding the central point at issue: that Trump has, indeed, become lethal to the party in many parts of the country. Mainstream conservatives will also learn that me-too Trumpian campaigns won't save them.

Republican members of the House and Senate in blue and purple areas will notice this. So will the party's leadership. Many now-timid GOP politicians might begin to worry less about losing primaries to pro-Trump candidates and more about how much damage their reckless, autocratic leader is doing to the party as a whole.

Local issues alone should inspire moderates and progressives to care about this choice. The candidates differ on taxes, climate policy, the fair drawing of legislative district lines, Confederate statues, Obamacare — and guns. This last cause alone should be enough to bestir citizens to the polls. The National Rifle Association would be no less gleeful than Trump over a Northam setback.

This competition might have been a more congenial affair. Northam is a middle-of-the-road Democrat in a long Virginia tradition who inspires great loyalty among those who have worked with him. Gillespie is a former lobbyist and GOP operative who can be quite amiable and almost lost the GOP primary because he was not in the Trump mold.

But Gillespie decided he could win only by injecting Trump's poison into his campaign. The antidote to noxious politics of this sort is to defeat it.

Read more from E.J. Dionne's archive, follow him on Twitter or subscribe to his updates on Facebook.