Here’s a familiar-seeming political tale. An incumbent Republican senator, from a famous political family and with a long history of moderation, is challenged by an upstart candidate in the GOP primary. The upstart is a successful entrepreneur turned talk-radio host and small-town mayor with a reputation for slashing spending and fighting unions; the Club for Growth endorses him. The Republican establishment rallies to the incumbent’s side. Karl Rove works for the incumbent; Mitch McConnell and John McCain stump for the incumbent. In the end, the incumbent wins, but barely. Then the incumbent goes on to lose to the Democrat in November in a race that may have tipped the balance in the Senate.

You might assume that this story refers to something from the 2010 or 2012 election cycles, when — so the narrative goes — tea party candidates caused all sorts of grief for the Republican establishment and potentially cost the GOP control of the Senate. But the details don’t quite fit any election in those years. Instead, this is the story of the 2006 Republican primary in Rhode Island. Lincoln Chafee was the incumbent; Steve Laffey was the upstart; Sheldon Whitehouse was the Democrat who beat Chafee that November, when Democrats took control of the Senate, 51-49.

With McConnell having defeated his challenger, Matt Bevin, in the Republican primary in Kentucky this week, there’s been a lot of talk about whether the influence of the tea party is waning. According to a series of mainstream media accounts, McConnell “crushed” the tea party in “the latest big beat” for the movement, which is “losing steam” as the economy improves.

There are a couple of problems with this story. The most important is that the tea party is hard to define. Take that Rhode Island race in 2006. Steve Laffey had all the hallmarks of what now might be called a tea party candidate. (Laffey, in fact, has now moved to Colorado where he is running for Congress and speaking to tea party rallies.) But the term wasn’t used in its current political context back then.

Furthermore, as Slate’s Dave Weigel pointed out earlier this week, the term “tea party” is applied very loosely by the political media. Was Missouri Rep. Todd Akin a member of the tea party, for instance? Weigel says no: Most groups associated with the tea party endorsed either Sarah Steelman or John Brunner in the 2012 Republican primary in Missouri. I think the case is considerably more ambiguous: Akin was listed as a member of the Tea Party Caucus on Michele Bachmann’s website in 2012. But these ambiguities arise all the time. Marco Rubio was once strongly associated with the tea party but is now somewhat estranged from it. Sometimes the term seems to serve as a euphemism for “crazy Republican” rather than anything substantive.

What is the tea party, exactly? That’s not so clear. There are a constellation of groups, like Tea Party Patriots, FreedomWorks and Americans for Prosperity, who sometimes associate themselves with the movement or are associated with it. But their agendas can range from libertarian to populist and do not always align. As in Missouri, they often do not endorse the same candidate. Nor do they always endorse the candidate who self-identifies as member of the tea party.

Is the tea party opposed to the Republican establishment or has it been co-opted by it? That’s also hard to say. The Tea Party Caucus no longer exists in a substantive way in the House. A group that called itself the Senate Tea Party Caucus did hold a meeting at some point last summer. The attendees included McConnell and McCain — those establishment stalwarts — who are therefore now listed as former members of the Tea Party Caucus at Wikipedia.

Perhaps it’s time to discourage the use of “tea party.” Or, at the very least, not to capitalize it as The New York Times and some other media organizations do. “Tea Party” looks better aesthetically than “tea party,” but triggers associations with a proper noun and risks misinforming the reader by implying that the tea party has a much more formal organizational infrastructure than it really does.

We got along perfectly well without the term. In 2006, nobody had a problem with describing Laffey as a “feisty conservative” challenger. In 2004, Rep. Pat Toomey, who nearly defeated Sen. Arlen Specter in the Republican primary in Pennsylvania, was “a conservative who has attacked Mr. Specter as a Ted Kennedy liberal too supportive of abortion rights and the United Nations,” according to The New York Times. That gets the point across every bit as well as describing Toomey as a “Tea Party candidate,” as the Times would when he ran again (and won) in 2010.

Nor is it clear that these challenges are becoming less common or less successful. The chart, below, depicts the share of the vote received by Republican incumbent senators in their primaries or party conventions dating back to 2004.

The downward trend in the chart is statistically significant as that term is usually defined (“statistical significance” is every bit as thorny of a concept as “tea party” — but that’s a subject for another post!). From 2004 to 2008, Republican incumbents got an average of 88 percent of the vote in their party primaries, compared to 78 percent from 2010 to 2012.

Has the trend reversed itself? So far in 2014, the three incumbent Republican senators to have had their primaries (these are McConnell, John Cornyn of Texas and Jim Risch of Idaho) received an average of 67 percent of the vote, a little worse than the party average in 2010 and 2012. Obviously, the sample size is small, and the data is fairly noisy. But that’s precisely the reason to avoid jumping to conclusions. For all the talk of the rise of the of the tea party, only three out of 19 incumbent Republican senators in 2010 and 2012 were defeated. (One of them, Lisa Murkowski of Alaska, went on to win the general election anyway as a write-in candidate.) That the so-called tea party candidate lost one race in Kentucky this year but got a much higher share of the vote than challengers usually do doesn’t tell us very much.

Whether the Republican Party continues its drift to the right — something that I don’t think should be taken for granted — is an important question. The evidence for it will manifest only noisily in individual races, however. Narratives centered on the rise and fall of the tea party may not give us a clearer perspective.