Here's how a get-out-the-vote operation generally works.

Campaigns look for a combination of two things: People who support their candidate and who will also vote. To bolster those numbers, a campaign identifies a geographic area with a high density of voters that are either hardcore supporters who don't vote very often or voters who vote all the time and can be persuaded to support the candidate. (The most effective form of persuasion is to have staff or volunteers deliver specific arguments to voters face-to-face, which is to say at their homes.) Since contacting people is pretty hit or miss, it's better to decamp in a location over an extended period of time to ensure you can talk to as many people as possible before voting begins. Then, when it does, you have a group of staff or volunteers who know the community well and, often, particular voters. (Campaigns put people in the field or on the ground, which is why this process is called "field" or "ground." Clever.) On Election Day (or during the early voting period) campaigns check to see who has already voted and hustle to get everyone else who meets that two-part combination out to the polls.

Normally, these efforts are less important for Republican candidates. Voting is habitual, and not moving around a lot means not having to re-register at each new place you live. Therefore the best predictors of voting regularly are age, income and home ownership -- demographic groups that lean toward the Republican Party. Democrats, however, have spent years working on get-out-the-vote, since their core demographics -- people of color and young people -- are less likely to make time to go to the polls.

The GOP has put a new effort into field in recent cycles, though. On Friday, the party announced a broad expansion of its on-the-ground efforts. The party was adding "an additional 392 staff and 98 new offices for its nationwide field organization," a press release read, "bringing the total number of paid RNC field staff across the country to over 1,000. The RNC’s field program has been in battleground states since 2013 and currently has more staff in the field than at any point in the 2012 cycle."

The announcement came shortly after a tweet from the party's presidential nominee, suggesting that estimates of his strength in the field were too pessimistic.

(Was he responding to Chris Cillizza's comments on MSNBC's "Morning Joe" about Trump's efforts in Florida? Maybe!)

In the past, Trump has said that he plans to defer to the party on field efforts, which would mean that one could read the GOP's announcement as showing a new strength on the ground for Trump. But there's a catch.

So let's say that you are running a campaign operation for the Republican Party in North Carolina. You have an incumbent senator, Sen. Richard Burr, who is in a close race for reelection and a close race for president. Early voting begins in late October.

Now let's say that, by early- to mid-October, it's clear that Donald Trump can't recover a national lead. Maybe it's still close in North Carolina, but he continues to trail by an average of 6.5 points in the ten closest states from 2012. It's clear, in other words, that he won't win. Let's say further that your incumbent senator does well with moderate independent women, a group with whom Trump doesn't.

What are you going to do? Are you going to spend your time sending volunteers to doors to convince them to consider Trump, or will you have them spend those precious seconds pitching Burr? When it comes time to get people to go vote, are you going to focus on sporadically-voting white working-class men, or on those moderate independent women who you might be able to spur to vote?

There's a lot of intricacy to the relationship between the party and the presidential candidate. But one reason campaigns like to run their own efforts is that they can be sure that their candidate will be the focus of outreach. If the GOP has limited time and resources to persuade and turn out voters, and they have to decide between a senatorial candidate who could win and a presidential candidate who can't, it's not a tough choice to make.

Put another way: Trump's putting his campaign's life into someone else's hands. It's unclear whether or not he realizes it.