(CNN)Midterm elections are about one thing: Base enthusiasm.
Unlike presidential elections -- where casual voters dial in and turn out -- midterm elections, historically speaking, tend to be the dominion of only the most committed party warriors. And those most committed party warriors almost exclusively hail from the extreme edges of both the Democratic and Republican coalitions -- i.e. the most liberal and the most conservative elements.
Which brings me to the chart above. It's from a brand new national Pew poll and shows one thing very clearly: The Democratic base is more passionate than its Republican counterpart about the 2018 midterms.
Almost 7 in 10 (69%) of Democrats say they are "looking forward" to the 2018 midterms, as compared to 58% of Republicans. Dig deeper and the enthusiasm gap widens. More than 8 in 10 self-described "liberals" are looking forward to the coming election, as compared to 61% of "conservatives."
A look back at the 2010 and 2014 midterms reveals why these numbers matter so much.
At this point in 2010, Republicans had a 15-point enthusiasm edge over Democrats as it related to the midterms. In 2014, it was a 12-point Republican lead. In 2010 and 2014, conservatives were overwhelmingly more likely to be looking forward to the election than liberals.
And, what happened in those elections? Massive across-the-board gains for Republicans -- everywhere from the state legislative level to the US Senate.
Why? Because, in each case, the GOP base was excited and motivated to turn out in midterm elections to send a negative message to then-President Barack Obama about his handling of health care -- among other things.
Now the shoe is on the other foot. Democrats are enraged at Trump's presidency and view 2018 as their first, best chance to make sure he knows it.
From the almost three dozen Democratic takeovers of Republican-held seats in state legislatures across the country to Doug Jones' landmark win in Alabama at the end of 2017, the enthusiasm gap between the two parties has been playing itself out on the ground, as well as in polls like this one from Pew.
The Point: Republicans have to hope they can find some way(s) to motivate their base between now and November 6. Because you can be certain that Democrats are, to borrow a phrase, fired up and ready to go.