STORM LAKE, Iowa — Senator Kamala Harris ordered tacos at a Mexican joint in Storm Lake (two chicken, one pork). She mingled with the masses at a New York-themed bar in Sioux City. (“You’ve got the whitest teeth,” one patron told her. “That’s a plus right there.”) She sampled apple egg rolls and flipped pork chops at the Iowa State Fair in Des Moines.

“I can also flip Republicans,” she grinned while gripping a metal spatula.

As Ms. Harris trundles her way across Iowa on a five-day bus tour that is her longest trip yet to any early primary state, the California Democrat’s embrace of Iowa’s quirky political traditions has delivered the unmistakable message that the state’s kickoff caucuses are increasingly central to her 2020 calculations after months of focus on South Carolina.

By the end of her tour on Monday, Ms. Harris will have made more stops in Iowa on this trip than she did in the entire first half of 2019, according to the Des Moines Register’s candidate tracker. She did not once venture farther west than the Des Moines suburbs until July, as her one planned trip there was scratched because of Senate votes.