Washington (CNN) A poll this week showed Democrat Ralph Northam with a 13-point lead over Republican Ed Gillespie in Virginia's race for governor.

Time for Republicans to make an all-out bid to win over moderates who are still on the fence, right?

Wrong.

President Donald Trump waded into the race for the first time Thursday night on Twitter with a message aimed squarely at the party's conservative base.

The President was parroting an attack that has played on repeat for weeks on Washington and Richmond TV stations. The ads have featured menacing-looking figures purported to be part of the MS-13 gangs and have prominently displayed the gang's "Kill, Rape, Control" motto.

The origin of the attack ad is a tie-breaking vote Northam, Virginia's lieutenant governor, cast in the state senate in January to defeat a GOP bill that would have banned sanctuary cities in Virginia. It was purely a pre-emptive vote -- the state doesn't actually have any sanctuary cities.

It's one of two attacks Gillespie, the former Republican National Committee chairman, is featuring prominently. The other one -- on a mailer this week -- blasts Northam over his position on Confederate monuments, saying he "wants to tear down history while making life easier for illegal immigrants."

Trump's tweet underscores the GOP's desire to turn the nation's most important race of 2017 into a culture war.

Because it happens in a swing state the year after a presidential election -- and because its law limiting governors to a single term means there are always new names on the ballot -- Virginia's governor's race is seen nationally as a useful barometer of a president's support a year into his term.

But the actual electorate is much different than it was a year earlier.

In the 2012 presidential election, 71% of Virginia's registered voters cast ballots. The following year, just 43% voted in the governor's race. From 2008 to 2009, the drop was 74% to 40%. That pattern has repeated itself in election cycle after election cycle, data from the Virginia Department of Elections shows.

Who participates in lower-turnout elections? Typically it's each party's most loyal and committed supporters -- not indecisive moderates.

That's why both campaigns are so focused on turning out their bases in the race's final month.

Trump isn't popular in Virginia, with just 33% of those polled saying they approve of his job performance -- a figure that could prove fatal to any Republican statewide candidate.

But Gillespie also has a Trump problem with his base. Among Republicans, 74% approve of Trump's job performance. But just 57% of Republicans said they believe Gillespie supports Trump a great deal or a good amount.

Among registered voters, 10% said illegal immigration is the biggest issue in the race, and 3% said Confederate monuments -- again, a small but important set of voters. And the vast majority of them are conservative: Among Republicans, 19% identified illegal immigration as the most important issue, while 6% said Confederate monuments. Among Democrats, those numbers were negligible.

The poll found registered voters are relatively unengaged. Only 58% are paying close attention to the race, and one in four said they could change their minds on who they support. Gillespie -- and Trump -- hope they'll catch their die-hards' eyes before November 7.