Beto O'Rourke, the Texas congressman who is the likely Democratic nominee to take on Sen. Ted Cruz this fall, recently tweeted proudly that he has an "F" rating from the NRA and has never gotten any money from them. Later, he tweeted a video stating his support for some form of universal, government-guaranteed health care. O'Rourke has lately been raising money faster than Cruz, and while the incumbent is still the favorite, it's a race Democrats increasingly think they have a shot to win.

Of course, if any Republican would be vulnerable in Texas, it'd probably be Cruz (watching him one is reminded of what the great Molly Ivins used to say about another Texas GOPer, Phil Gramm: "Even his friends don't like him"). But what's most notable about O'Rourke's candidacy isn't just that he has a shot in this deep red state, but that very few people seem to be telling him that what he really needs to do is reach out to the center. O'Rourke may not win, but if he does it's going to be due to the way he's running an unapologetically liberal campaign meant to energize Democratic voters.

That is increasingly what the Democratic Party as a whole seems to have decided. While there are some narrow circumstances when nominating someone with moderate views on this or that issue might still be a good idea, Democrats have at long last come around to the strategy Republicans have used for decades. Success in American electoral politics today is achieved not by "reaching out" to the center but by running campaigns that make the voters who already agree with you excited.

Okay — time for some game theory (really). For a long time, Democrats acted according to a political science concept known as the Median Voter Theorem, whether they knew it or not. It states that the outcomes of the political system will reflect the preferences of the median voter, so if you move too far to the right or the left, you'll find yourself farther from that voter than the other party, lose her support, and ultimately lose the election. You don't actually have to give the median voter exactly what she wants, you just have to position yourself closer to what she wants than the other candidate.

The problem with the Median Voter Theorem is that like many economic models applied to politics, it depends on a series of assumptions that aren't actually true in the real world, including the facts that there isn't one left-right dimension to politics and the body of voters isn't a given before the campaign starts.

But for a long time, a powerful segment of the Democratic Party believed that if Democrats lost elections, the answer was to move toward the center and capture that median voter. This was the rationale of Bill Clinton's "Third Way," which presented an ideological program to the left of Republicans but to the right of traditional Democratic liberalism — in other words, straddling that median voter. It seemed to work — sometimes, anyway.

But win or lose, Republicans never lost faith in the opposite theory: that what really matters is getting your own voters to the polls. They might have the occasional candidate who found ways to appeal to moderates (like George W. Bush with his "compassionate conservatism"), but it was never at the cost of ideological compromise. Even when they lost, they rarely concluded it was because they had moved too far to the right. Indeed, they kept moving farther and farther, and paid no apparent price at the ballot box.

That's because they were moving right at the same time the country was becoming more polarized and the parties were growing more internally unified. After Democrats embraced the cause of civil rights in the 1960s, the parties became more ideologically consistent, with large numbers of conservative Democrats (especially in the South) moving to the GOP and liberal Republicans simply fading away. In the bipolar world we live in today, any move to the center risks alienating people in your own party, who might respond by staying home.

Nobody learned a harder lesson about the impermeability of party boundaries than Hillary Clinton. In 2016 she thought that she could win over moderate, sensible Republicans appalled that their party had nominated an orc in a hairpiece, but she turned out to be wrong. Donald Trump suffered no more defection from Republicans than Mitt Romney had four years before, and got enough conservatives out to the polls in order to prevail.

The Democratic Party's new realization doesn't mean there aren't still going to be intra-party battles between the left and the far left in primaries, because there will be. There are old Bernie Sanders supporters eager to turn every primary into a re-run of the 2016 Hillary/Bernie throwdown, and there are party operatives still working off the Median Voter Theorem and counseling ideological moderation.

But the prevailing trend is for Democratic candidates everywhere — even in places like Texas — to be asking themselves what will get their own supporters the most revved up about voting. The answer will often be a full-throated liberal agenda, one that includes universal health coverage and even gun restrictions, which until recently many Democrats were terrified of proposing. It might be working in Texas, where early voting for the primary has increased by 90 percent over 2014 and is even higher than it was in the presidential year of 2016.

It also means that "electability" — which is often a term for trying to figure out what will appeal to that median voter — will (or at least should) be much less of a concern for Democratic presidential primary voters in 2020 than it has been in the past. The consequence could be not only a field of candidates who all take proudly liberal positions, but a Democratic electorate that's eager and excited to go out and vote for the nominee.

That's no guarantee of success; we have no idea what will happen over the next two and a half years and how it might affect Donald Trump's re-election bid. But it doesn't look like Democrats are going to be chasing the median voter again, at least not for some time to come.