BOONE, Iowa — New Jersey Sen. Cory Booker sat in the driver’s seat of a red, white, and blue Winnebago RV last week, admiring the charm of Iowa’s vast landscapes out his window, playing DJ, and jamming to tunes like "Born to Run," "American Pie," and "Sioux City Sue" (the last of which was coincidentally the name of the Winnebago).

"I’m not liking Iowa, I’m loving Iowa," Booker told NBC aboard the RV as he sped through multiple stops on a multi-day tour of the area. "This is an amazing state. I owe my very existence to this state. This is the state my grandmother was born in. She came from a coal mining family. She was born and raised in Des Moines."

On top of attending a family gathering, Booker's official reason for his recent Iowa trip was to campaign for local candidates down the ballot this fall. Behind the wheel of that RV was J.D. Scholten, the Democrat challenging Iowa’s rabble-rousing Republican Congressman Steve King. Scholten was happy to take advantage of the extra attention Booker brought to his campaign, while Booker made him a star of his near-constant Instagram story updates from the road.

The calendar may say it’s 2018, but underneath the layers of midterm campaigning this year is the invisible contest for 2020. As with so many other moves of big-name Democrats around the country this fall, where they are and what they’re doing could be interpreted as helping to slowly build framework for a future run for the White House.

Sen. Elizabeth Warren’s decision to release her DNA test results on Monday was interpreted by many as about more than just her current quest for re-election in Massachusetts. Sen. Kirsten Gillibrand of New York, another senator seeking re-election this year, was seen campaigning for Michigan Democratic candidate for governor Gretchen Whitmer. Sen Bernie Sanders announced a 15-city blitz ahead of the midterms. Former Vice President Joe Biden has been back traversing the political trail for months.

It’s now no longer just the lesser-known tier of names circling the first presidential primary voting states of Iowa and New Hampshire. Kamala Harris is also set to visit Iowa next week. South Carolinians already say they’re getting "swarmed" by a crew of potential presidential contenders.

And much of the 2020 movement isn’t as visible as touching down in a state with a caravan of cameras tagging along.

"Right now there’s a lot of activity where some of these people are reaching out to the main activists, and these are sort of the elected officials or maybe chairs from previous campaigns," explained Neil Levesque, the Executive Director of the New Hampshire Institute of Politics at Saint Anselm College, while hosting Flake's recent appearance. "There are a lot of phone calls going back and forth, and some visits here to New Hampshire like we see today."