SIOUX CITY | Every time a presidential candidate makes a stop at a cafe, school or business, it is an opportunity to drive more people to support their campaign.

With that simple principle as the driving point, presidential candidates have visited Northwest Iowa in large numbers over the last 10 months. It began with a trickle in March 2015 and turned into a flurry this month, as they try to drum up support for the all-important, first-in-the-nation, Iowa caucuses on Feb. 1.

"Everybody has had a wealth of opportunities to see somebody if they wanted to," Sioux County Republican Party Chairman Mark Lundberg said.

A review of campaign stops through Saturday showed 139 events had been held by the existing 15 candidates -- three Democrats and 12 Republicans -- in 15 Northwest Iowa counties. Other candidates, such as Rick Perry, Bobby Jindal, Jim Webb and Scott Walker, held campaign events before dropping out.

Over the last 11 months, candidates have stumped in Sioux City and throughout Northwest Iowa, as far north as the Minnesota border, as far east as Sac County and as far south as Monona and Crawford counties.

Northwest Iowa is rich Republican turf, and the overwhelming number of candidate stops have been by Republicans, with 120 events. The three Democratic candidates -- Hillary Clinton, Bernie Sanders and Martin O'Malley -- have combined for 19 events.

The candidates campaigning the most in Siouxland have been Republicans Rick Santorum with 29 events, Mike Huckabee, 25, and Ted Cruz and Carly Fiorina, with 17 each. But a large number of campaign stops in the area hasn't necessarily resulted in big results, at least as shown by Iowa polls. Of the four, only Cruz is among the top-polling Republicans in Iowa. The Texas senator is locked in a tight fight with Donald Trump, the national front-runner in the GOP race. Santorum, Huckabee and Fiorina have been mired in low single digits in most polls.

On Thursday in Sioux City, Huckabee said there are no short-cuts to doing well in Iowa, so numerous retail campaign stops are needed. Buena Vista University Professor Bradley Best said that old Iowa campaign saw is being tested, since Trump, who has "global celebrity status," has made only four stops in Northwest Iowa, including a rally Saturday in Sioux Center.

"A couple of the candidates who have struggled so badly on the Republican side have nonetheless made a very large number of campaign stops in Northwest Iowa. What that demonstrates is that frequency of on-the-ground campaign stops does not ensure success in the polls and, conversely, failure to engage in frequent campaign stops -- Donald Trump would be an example of this -- does not doom one to failure or to a low ranking in polls," Best said.

Among the dozens of trips, there have been some surprising decisions by some Republicans to essentially bypass Northwest Iowa. Former Florida Gov. Jeb Bush, a son of one president and the brother of another, made one stop in Sioux City in July but hasn't been back in Siouxland since. Ohio Gov. John Kasich also has only visited Siouxland once, while New Jersey Gov. Chris Christie has held three events. Republican Jim Gilmore is the other announced candidate who has not traveled to the area at all.

Gov. Terry Branstad said he's personally advised Bush to campaign more heavily in Iowa, since "the more time you spend, the more people you see, the better you do."

"I've never lost an election. I think I know this state pretty well, and I think those people who have chosen not to come to Northwest Iowa have made a huge mistake," Branstad said.

The governor noted in his past general election races, he captured more than 90 percent of the vote in Sioux County, the most Republican of Iowa's 99 counties.

Best said candidates make very strategic choices on where they will campaign, to help their chances to win the overall nomination by the time of the summer national party conventions. For some, Iowa has a diminished role in that quest, as some candidates focused more on New Hampshire, which has a primary on Feb. 9.

"Many of them believe or suspect that they will not suffer badly for de-emphasizing Iowa and shifting their energies and their efforts in the direction of New Hampshire and South Carolina, subsequent primaries," Best said, echoing a point Branstad also made.

Among Democrats, former Maryland Governor O'Malley leads the way with eight stops in Northwest Iowa, followed by U.S. Sen. Sanders with seven and Clinton with four. All four of the former secretary of state's stops have been in Sioux City, while Sanders and O'Malley have visited Sioux City and some smaller cities in the area.

Buena Vista County Democratic Party Chairman Jim Eliason, of Storm Lake, said he was grateful Sanders and O'Malley took time to travel to Storm Lake, home to Buena Vista University. He said people prize the ability to see a person in their midst.

"We would have liked to have seen (Clinton) out here. Is it disappointing? A little," Eliason said.

There were months with just a sparse few candidate events in the region -- back in March, April, May as things got started, and later in September, had just four or fewer campaign stops. The bigger months were July, August and October, then the final surge came with 21 in December and 42 in January (as of Jan. 18 announcements).

The candidates have primarily stopped in Sioux City, with 41 events, but many surrounding towns also have been visited with frequency. The list with a half-dozen or more includes Sioux Center (11), Storm Lake (10), Orange City (nine), Le Mars (eight), Denison (eight), and Sheldon, Spencer and Rock Rapids with six each.

"They are just going to where they think the most friendlies are," Lundberg said.

Best said those events outside Sioux City show the candidates recognize they know where to go to tap places largely populated with Protestant evangelical voters.

"(Evangelical voters) are seen as a lever that has to be pulled in their favor in order to win the nomination," Best said.

The smallest town to host a candidate was Cushing, when Fiorina spoke to more people in the fire hall than live in the Woodbury County town of 220 people. Cruz visited Pierson, population 366, another Woodbury County town. He spoke at a picnic where he formally received the endorsement of state Sen. Bill Anderson, R-Pierson.