Historically, Iowa has been a swing state. Since 1972, Iowa voters have cast their presidential election ballots for Republicans six times and for Democrats six times.
Looking at the three most recent presidential elections, Iowa voters in 31 out of the state's 99 counties elected Barack Obama twice, and then switched to elect Donald Trump in 2016. This partisan flip-flop has earned these counties the title of "Pivot Counties, according to BallotPedia.
This pivot was mostly seen on the eastern half of the state, and includes counties surrounding the Quad Cities: Dubuque, Jones, Jackson, Clinton, Cedar, Muscatine, Louisa, Des Moines, and Lee Counties. Scott County did not pivot.
In Illinois, 11 of the state's 102 counties are considered pivot counties. This includes mostly counties surrounding the Quad Cities: Mercer, Henderson, Warren, Knox, Fulton, Henry, Whiteside, Carroll, and Jo Daviess Counties. Rock Island County did not pivot.
Scott County in Iowa and Rock Island County in Illinois have consistently turned in Democratic selections since 2012.
Here's what the chairs of each county party had to say about that:
Drue Mielke, Rock Island County Republican Central Committee Chairman:
"In 2016, the 17th Congressional District. of which Rock Island County is located in the center, carried President Trump. The more conservative voters who live in the 17th Congressional District do live outside of Rock Island County. The Trump margin in Rock Island County was a much smaller percentage than the prior Republican candidates.
The Republicans in Rock Island County are fielding two strong county-wide candidates who have large Democratic support- Kathleen Bailey for State’s Attorney and Brandi McGuire Madunic for Circuit Clerk. This year looks to be a the year the Rock Island County pivots."
Derek Jones, Rock Island County Democratic Central Committee Chair:
"I would guess that many of those counties were already generally trending Republican, but President Obama got a boost because Illinois is his home state. Hopefully, these counties will ultimately realize that wealthy corporations and their Republican enablers are not benefitting small towns in Illinois, and will turn back to the Democratic Party, which will continue to fight for good wages and a strong social safety net to help us weather the difficult times. I also believe the leadership and great work from our local Democratic elected officials also help instill that trust of the Democratic Party and our Presidential candidates."