Talk of a tea party takeover of American politics -- or the Republican party -- has faded of late.

James Manship (L), in costume as George Washington, and William Temple, in colonial costume, chat at the Conservative Political Action Conference (CPAC) in Oxon Hill, Maryland, March 8, 2014. REUTERS/Mike Theiler

Republican Senate Leader Mitch McConnell has declared open war on outside groups -- like the Senate Conservatives Fund -- who provide the financial backing for tea party challengers to sitting incumbents.  Tea party-aligned primary candidates have fizzled. In a recent NBC-Wall Street Journal national poll, just 23 percent of people had a positive image of the tea party while 41 percent had a negative impression -- the worst numbers for any individual or group tested other than Russian President Vladimir Putin.

Simply put: It's easy to write the "Tea Party is dead" story. But, according to a fascinating new project  out of the Brookings Institution that aims to study the 2014 primary season (more of this please!), the tea party remains relevant -- largely because it supplies the vast majority of candidates willing to take on sitting Republican incumbents at the federal level.

Image courtesy of Brookings

Writes Brookings' Elaine Kamarck of the findings:

We looked at all the Republican primary challengers in these first two states and categorized them according to ideology.  As is clear, the Tea Party is the dominant source of challenges in Republican primaries.  For those who are hoping they will just go away the presence of Tea Party inspired candidates (and their close cousins, Libertarians) means that the Ted Cruz and Rand Paul wings of the Republican Party are alive and well.  They may not win many elections, and they still have a hard time recruiting talented candidates; nonetheless next year’s Republican members of Congress will be paying close attention to them.

A few caveats worth noting:

1. We are two states into the primary season. That is, as Brookings' acknowledges, a very small sample size from which to draw conclusions.

2. Running against incumbents is not the same thing as beating incumbents. While challengers -- no matter their ideological affiliation -- will never have a 50-50 chance at beating an incumbent, simply rolling out a bunch of candidates aligned with the tea party who have no chance of winning doesn't equal real influence on the party and its nominees.

The test for the tea party as the primary season continues then is not whether they can field GOP candidates but whether some of those candidates can win.  If they can't, recruiting becomes more difficult. And, without adding to their ranks among elected officials, the tea party movement runs the risk of stagnating or beginning to backslide.  Of course, for all of the struggles of the tea party at the federal level so far in the 2014 cycle, there have been several instances at the state level where candidates aligned with the tea party have done quite well. (Texas jumps to mind.)

Politics -- and political movements -- are sustained and strengthened by one thing: Winning. The tea party is not immune from that iron-clad rule.