President Trump and Republicans are eager to undercut the idea that a wave election is forming for Democrats. Trump made that case in two tweets on Tuesday night, first declaring that the Democratic Party is “in turmoil” because … well, it wasn’t clear. Then he retweeted a comic showing himself wearing star-spangled board shorts as he surfed a killer red wave.

Republican Party spokeswoman Kayleigh McEnany joined the fun, tweeting that Rep. Joe Crowley’s (D-N.Y.) loss in the Democratic primary in New York’s 14th Congressional District was somehow an indicator of a “red tsunami” rather than a blue wave, as though a Democrat losing a primary to another Democrat meant that no Democrat could ever again hold that seat.

Bad news for her party, given that two Republican incumbents have also lost primaries this year.

The idea that a “blue wave” is forming for November is based on a few things: The historic trend of a new president seeing his party take a hit in Congress in his first midterm election and, of course, polling that continues to show Democrats with an advantage on the generic congressional ballot. What constitutes a “wave” is subjective, and we can be confident that, regardless of the outcome in the fall, the debate over whether it was a wave will fall along mostly partisan lines.

What’s worth noting about Crowley’s loss is not anything about a blue wave approaching for November. Replacing a Democrat with a Democrat (there’s no way a Republican wins the 14th District, which voted for Hillary Clinton in 2016 by a more than 3-to-1 margin) doesn’t tell us a whole lot about what to expect in November. But it does serve as a reminder that a blue wave has already crashed in American politics — drenching Crowley’s Democratic Party.

The winner of the race in the 14th District, as you have no doubt already heard, was Alexandria Ocasio-Cortez, a woman of Puerto Rican descent who ran a smart campaign and beat Crowley handily. But she’s also a Democratic Socialist, a member of the surging left-most wing of the Democratic Party and an advocate for a swath of progressive measures like Medicare for all and a jobs guarantee.

When Sen. Bernie Sanders (I-Vt.) first threw his hat into the ring for the Democratic presidential nomination in 2016, there was a spate of polling about whether someone with his self-described political leanings — again, a Democratic Socialist — could actually win. In a May 2016 poll, Gallup found that only 35 percent of Americans had a positive view of socialism, broadly — but that among Democrats, the figure was 58 percent. For context, capitalism was viewed positively by only 56 percent of Democrats.

Among those ages 18 to 29 — a group that includes Ocasio-Cortez — 55 percent viewed socialism positively, compared to only 24 percent of those 65 and older.

What Sanders both revealed and helped shape, though, was not an emergence of a Socialist party in the United States. Instead, it was a rising trend within the Democratic Party to embrace more progressive and more liberal policies. As many have noted, Sanders helped provide a mainstream set of policies that more traditional Democrats wound up supporting. Why? Because the base of the party was shifting under their feet.

We keep coming back to this graph, because it’s critical to understanding the party at the moment.

In 2000 — not that long ago — the number of Democrats who described themselves as conservative was about the same as the number who described themselves as liberal. Since, there’s been a steady push to the left; according to Gallup, half of the party now describes itself as liberal.

That’s the original blue wave.

Part of that shift is a function of less-liberal Democrats leaving the party and becoming independents. But the percentage of Americans identifying as Democratic only fell 5 percentage points from 2000 to 2017, according to Gallup data. There’s been a genuine surge in self-described liberals over the past two decades, from about 19 percent in 2000 to 26 percent last year. By contrast, 35 percent of the country identifies as conservative, down slightly from 2000.

In other words, there is a real appetite within the Democratic Party for liberal policies like those espoused by Ocasio-Cortez and Sanders. New York’s 14th District and Vermont are hardly moderate places, but when half of your party identifies as liberal, it seems clear that more-liberal policies will likely find an audience in less-liberal places. Increased political polarization suggests that more-liberal Democrats would likely end up earning support from more-moderate Democratic voters in general elections simply because of distaste among Democrats for Republican candidates (and vice versa).

Most of the Democrats who win primaries and then win election in November will not be as progressive as Ocasio-Cortez. Should the Democrats surge to victory, the new Congress will not be one in which Democratic Socialists are swarming the halls of power. But it will certainly be a more progressive Democratic caucus than the one that’s there or, probably, any in the last century.

The size of any wave in November is to be determined. The depth of its blueness has to a large extent already been established.