(CNN) President Joe Biden took his first big trip as president this week when he went to Wisconsin for a CNN town hall. The fact that Biden chose to go to Wisconsin shouldn't be lost on anyone. He will likely be going to the state a lot as president.
Arguably, no state tells us more about Biden's or any president's political standing in the last 30 years than Wisconsin. It's also likely to tell us whether his party does well in the 2022 midterms.
If you wanted to know who won the presidency in the last three elections, you needn't look further than the Badger State. It was one of just three states that voted for Biden in 2020, Donald Trump in 2016 and Barack Obama in 2012 (the other two are the key battlegrounds of Michigan and Pennsylvania).
But Wisconsin's importance goes deeper than just this fun tidbit of trivia.
Wisconsin was the state that put Biden to the 270 electoral vote threshold in the Electoral College. Had Biden carried every state he won by more than his 0.63 point margin in Wisconsin, he'd have been at 269 electoral votes. Put another way, Wisconsin got Biden the presidency.
Similar math holds for Trump in 2016. Wisconsin was the state that got him to and over 270 electoral votes, unless we count faithless electors.
Now, look at every election since 1992.
We'll do so by comparing the margin in every state in every presidential election to the margin in the state that put the winning candidate over the top in the Electoral College in that same election (just like Wisconsin has done in the last two elections).
We'll call this measure the swing state index. A swing state index close to zero in any election means a state is really important in a given presidential election.
Since 1992, the absolute value of Wisconsin's swing state index has averaged 1.3 points. No other state has had an average absolute swing state index closer to 0, which equates to Wisconsin being the state that has told us the most about where the Electoral College stands on average since 1992.
Further, Wisconsin is one of only two states (along with Pennsylvania) that has had no election in which the swing state index has been larger than +5.0 points or smaller than -5.0 points since 1992. This is another indication that Wisconsin has pretty much always been a state that you can count on to give you a good read of the presidential election.
If Wisconsin is close in an election, you can bet the overall election is also close.
The ability to be a consistent swing state is rare. For instance, the swing state index in Tennessee in 1992 was 0 (i.e. the state that put Bill Clinton over the top in the Electoral College). In 2020, Tennessee's swing state index was -24 points (i.e. way more Republican). Georgia's swing state index swung wildly from -4 points in 1992 to -14 points in 2004 to -0.4 points in 2020.
Wisconsin has maintained its swing state status, even as coalitions within the state have changed dramatically.
In 1992, the swing state index was -0.3 points or very close to being the state that put Clinton over the top in the Electoral College. Clinton's coalition spread across the state from urban to rural areas with 36 of the state's counties voting more Democratic than the state as a whole and 36 voting more Republican than the state as a whole.
But just as tiny populated rural areas became more Republican and highly populated urban areas became more Democratic nationally, so too has this been the case in Wisconsin.
In 2020, just 14 of the state's 72 counties were more Democratic than the state as a whole. Biden won in large part by crushing it in Dane (which contains Madison) and Milwaukee counties.
Of course, there won't be any presidential elections for a while.
Beyond the battle for the top spot in our nation's government, Wisconsin has proved a useful barometer in down ballot races over the last 15 years and could be a key state in the 2022 midterms.
The state elected a Democratic governor in 2006 and 2018, which were both good years for Democrats. In-between, Scott Walker won terms in the midterm elections of 2010 and 2014.
We'll see if Democratic Gov. Tony Evers is able to win reelection in 2022.
Likewise, the state has gone back and forth in who it elects to the Senate. Senate Democratic candidates have won in 2006, 2012 and 2018, which were all good years for Democrats. Republican Sen. Ron Johnson emerged victorious in 2010 and 2016.
Johnson, if he chooses to run, is on the ballot in 2022, and it's a state Democrats are hoping to flip. Johnson losing could signal that Republicans are in for a long night.
Ultimately, Wisconsin could hold the key for Biden in the final two years of his first time. A Biden presidency with a Republican-held Senate will be far more difficult for him to navigate.