(CNN) Midterms are a base election, but how big is Trump's base? We all know he brags about being the most popular president in the Republican Party (more popular than Abraham Lincoln, he says!). In the most recent CNN poll conducted by SSRS, the President's approval rating was 36%, which is not a record low, but not very good either.

But there are a number of ways to look at the available polling and election data to determine who exactly supports Trump and what portion of the population they represent.

In that CNN poll, he was under water with most of the population, but among Republicans his approval was at 82%, where it has been fluctuating since the beginning of his term. But the number of Americans who identify with a party has been on the decline. And while Republicans currently control every lever of power in Washington, they represent a smaller portion of the population than either Democrats or independents, although many independents may lean toward the GOP.

Pew Research tracks party identification with the most recent numbers showing a quarter who say they're Republicans, 31% Democrats, and 38% independents. There hasn't been a lot of fluctuation in recent years, except a small bump in 2016 (competitive primaries often cause this).

The US system, however, really only offers two options, so while fewer people identify with parties, those are the options they have on Election Day. That's, in part, how someone like Trump can lose the popular vote, but win the Electoral College. So does half of the country approve of the job he's doing? Did half the country vote for him? Again, not exactly. The 82% of the Republicans who approve of the job he is doing only translates to 20% of the country, overall.

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