The tea party has left a major mark on the 2012 Senate race landscape. Or has it?

Republican primary upsets won by candidates once viewed as underdogs (or even complete non-factors) in Missouri, Nebraska, Texas, and Indiana have brought renewed attention to a movement that altered the 2010 midterm environment.

But how much credit does the tea party deserve for a roiled Senate landscape? Not as much as you might think.

The tea party has made a difference in some Senate races, but hasn’t mattered as much in others. (Julie Jacobson/Associated Press)

Let’s start with what we mean by tea party. The movement is characterized by strict deference to the constitution, limited government and low taxes and spending. Activists also tend to be leery of longtime government insiders.

In Missouri, Rep. Todd Akin won an unlikely victory in a three-way Republican race on Tuesday. As a limited government conservative, Akin’s profile can aptly be described tea-party friendly.

But that’s only part of the story.

Consider that he ran against two other candidates who weren’t exactly longtime government insiders with their backs turned on constitutional principles. One was John Brunner, a political newcomer from the private sector who was a free enterprise advocate calling for less government. The other was Sarah Steelman, a former state treasurer backed by Sarah Palin who openly courted conservative support.

So what happened? Akin (the only GOP candidate who was also a member of Congress) was boosted by $1.7 million worth of indirect Democratic assistance. Democratic party strategists decided Akin’s unpredictable and ardent social conservatism made him the most desirable general election opponent for Sen. Claire McCaskill (D). So they aired TV ads boosting his credentials.

In Nebraska, Deb Fischer’s out-of-nowhere victory also came in a three-way GOP primary. There, she won not as the result of a longtime conservative push to elect her, but as the beneficiary of an expensive air war between establishment-backed Attorney General Jon Bruning and state Treasurer Don Stenberg’s national conservative allies, namely the Club for Growth and Sen. Jim DeMint (R-S.C.).

That’s the same Fischer who voted to raise the state's gas tax and override a veto of a bill to increase spending — hardly the calling card of a tea party candidate.

Indiana and Texas, on the other hand, are examples of races in which the tea party did have a notable influence. Local conservative activists met with Sen. Richard Lugar (R-Ind.) at the start of the cycle to express their unhappiness with his positions. When he declined to change course, they rallied around a Lugar-alternative, Richard Mourdock. Mourdock’s unapologetic conservatism brought him a subsequent wave of national support. And he cruised to victory over Lugar in May.

In Texas, Lt. Governor David Dewhurst’s presence in the 113th Congress once looked like a sure bet. But that was before Ted Cruz, a constitutional conservative running to Dewhurst’s right, caught fire. Dewhurst’s deep ties to state government also stoked doubts about his candidacy. He lost to Cruz in a runoff last month.

What about other races once believed to be top targets for the tea party? Utah was at the top of the list 18 months ago. As it turned out, Sen. Orrin Hatch was never really challenged. He prepared diligently for the conservative backlash and relied on the strength of a robust counter-operation. It worked.

In Michigan, Republicans nominated Pete Hoekstra, a former congressman who had worked for a lobbying firm. In Pennsylvania, they nominated a former Democrat. In Wisconsin next week, the latest polling shows moderate former governor Tommy Thompson, who has spent time on the lobbying circuit, is leading first-time candidate Eric Hovde and conservative former congressman Mark Neumann.

Often, races are too nuanced to peg as tea party-vs.-establishment or insider-versus-outsider. Consider the Republican election in Arizona, which will take place at the end of the month. Businessman Wil Cardon is running against Rep. Jeff Flake. Is Cardon the decided tea party outsider in the race? No. Flake’s brand of strict fiscal conservatism has brought him plaudits from limited government conservatives.

It would be a mistake to conclude that the tea party has not had an influence on the Senate landscape in 2012. It indisputably has. But to neatly sum up every unexpected win or conservative victory as evidence of immense tea party enthusiasm would also be incorrect.