Sen. Bernie Sanders (Vt.), then a presidential candidate, speaks at a rally. (Matt McClain/ The Washington Post)

After Barack Obama won the White House in 2008, the tea party was born. It was a mixed blessing for the Republican Party, providing much-needed enthusiasm while also instilling fear in Republicans to toe the ideological line.

The result was a GOP that won elections but became rigid, polarized and more bottom-up than top-down. The tea party eventually came to connote Republicans' move toward the political extreme, but it has clearly made an impact.

The question is, now that a Republican is returning to the White House, will a similar movement spring up on the Democratic side? It has been asked plenty in recent weeks, including by Vice, the Guardian and Salon.

Some might say it already has, given Bernie Sanders's success in the 2016 Democratic presidential primary. But new data from the Brookings Institution suggests a rising tide of progressivism has yet to register where it arguably matters most: in congressional primaries. And in fact, it might have even taken a step back last year.

A quick history lesson: House and Senate primaries are where the tea party made its real impact, putting the fear of God into Republican incumbents and candidates worried about their own political futures and “getting primaried.” By knocking off just a few incumbents and establishment Republicans in 2010 and a few more in 2012, the tea party forced every Republican member to look over their shoulders. The vast majority of them had no worries about losing the general election in their safe districts, so foreclosing a primary challenge was really their only political survival concern.

To this point, though, liberals just haven't rallied the troops for a similar effort. As the Brookings reports show, progressives are defeating fewer establishment candidates, and the voters who turn out for contested primaries just aren't as conducive to a tea party-esque effort to redirect the Democratic Party toward the political left.

A few charts tell the tale.

First is the simple fact that fewer progressives seem to be running. Brookings took on the Herculean task of categorizing every single 2016 primary candidate by whether they were more establishment-oriented or more conservative/tea party or progressive.

On the Democratic side, less than 30 percent of candidates fit the “progressive” label, while about half were “establishment. It was reversed on the GOP side, with only about one-quarter being “establishment” and nearly 6 in 10 being either “conservative” or “liberal.”

This is a subjective study, of course, but even accounting for that subjectivity, there doesn't seem to be a cadre of progressive candidates stepping forward to pick up the torch Sanders has lit. At least not yet.

Chart 3

Next is the success rate. The only two House Democrats who lost congressional primaries in 2016 were both scandal-plagued ones, owing their losses to their own personal problems and not their ideologies. The progressive tea party, in other words, is still awaiting its first scalp — the one that will send a message to other Democratic incumbents to worry about their own primaries.

And if you look at progressive candidates writ large — both incumbents and challengers — their win percentage actually dropped between 2014 (67.9 percent) and 2016 (52 percent). Again, subjective, but a big shift.

There's also the fact that Democratic primary challenges just seem to be less effective. Brookings calculated the average margin of victory in contested primaries for GOP incumbents versus Democratic ones. And Republicans won, on average, by a narrower margin (about 52 points) than Democrats (about 64 points).

Republicans were also more likely to be challenged in the first place, with just 49 percent facing uncontested primaries, versus 61 percent of Democrats. So fewer Democratic challenges and less successful ones.

Given all that, it's worth asking whether progressives even have a shot at making this happen — at making their presence felt throughout the party in congressional primaries. And there's reason for skepticism on that count.

A separate new Brookings report features unprecedented data from Edison Research, the national exit pollster, which conducted exit polls on congressional primaries explicitly for Brookings. What it found is that Democratic electorates are less ideologically tilted toward the extreme and less interested in political purity.

In 2016, 78 percent of voters in competitive Republican primaries said they were more conservative than most general election voters in their districts. On the Democratic side, the number saying they were more liberal was just 67 percent. And 27 percent of Democratic primary voters actually said they were more conservative than their districts.

Similarly, while 42 percent of GOP primary voters said “shares my values” was the candidate quality that mattered the most, just 28 percent of Democratic primary voters said the same. Democrats were more interested in having the right experience and empathy.

These are all key markers when it comes to the success of ideologically spurred primary challenges.

All of this, of course, is in the past. And Sanders really got off the ground perhaps too late for a real progressive wave to hit Democratic primaries in the 2016 election. Maybe it'll pick up now that Donald Trump is in the White House.

But the above data comes even as the tea party is in decline, and it doesn't suggest a Democratic primary electorate that is clamoring for similar primary challenges. We'll just have to see.