ANALYSIS: Trump faces early referendum in Georgia congressional race

The race to fill an open House seat in Georgia has national implications.

But there's no choice.

A special election to fill an open House seat is happening today in a suburban Atlanta district that, although Republican, went for Trump in November by the slimmest of margins.

The national implications of the race have only grown in recent days. Both Republicans and Democrats have poured resources and attention into the election in hopes of sending a message that will reverberate to any other one-off special elections and beyond to 2018.

The momentum has been behind Democrat Jon Ossoff, who is facing down 11 Republicans in a field of 18, although the chance of any candidate – much less a Democrat in a Republican district – avoiding a runoff by clearing 50 percent in the first round seems remote.

“If you don’t vote tomorrow, Ossoff will raise your taxes, destroy your healthcare, and flood our country with illegal immigrants,” Trump said.

If the president's message seems grave, he has reason to sound alarms.

This is a Republican-heavy, upscale suburb that was skeptical of Trump before he became president, back when few thought he could actually win against Clinton.

Given the tumult of Trump’s first 89 days in office, few would argue he’s in a stronger position now than in November. That’s the message other Republicans are likely to draw from this race, as a snapshot of the president’s political standing, in one tiny swath of a state he carried.

Possibly more problematic for Trump, however, is how a loss in this race could affect his ability to govern in an environment where he needs his own party to fear as well as love him.