To outsiders — and many Republican insiders — the Tea Party looks insanely fratricidal. But there is a method to the Right's madness. The real question is how often the method pays off.

Look at Mississippi, where six-term Sen. Thad Cochran is one step closer to being the first major Republican incumbent to lose to a Tea Party primary challenger this year. Cochran received fewer votes than Chris McDaniel, the Republican state senator running against him. Neither candidate broke 50 percent, so the race is headed to a runoff, where recent history hasn't been kind to establishment candidates.

Conservative groups spent more than $5 million trying to unseat Cochran, with the Club for Growth chipping in $2.5 million. Much of that has been spent on hard-hitting — and occasionally misleading — ads. But the incumbent hasn't been bereft of outside support either. When a pro-McDaniel blogger creepily snuck into a nursing home to videotape Cochran's bedridden wife, the National Republican Senatorial Committee eagerly fanned the flames of the story and tried to link the event to McDaniel's campaign. (So far no connection has been conclusively established.)

All this has led some Republicans on both sides of the Cochran-McDaniel fight to ask: Is this a good use of party resources? The two men would likely have very similar voting records in the Senate. Both should be heavily favored against the Democrat. Why not just settle for Cochran and avoid this intramural spat?

Here's why: Conservatives don't just want to elect candidates who have the letter "R" next to their names. They want to accomplish certain policy goals. The chief objective animating the Tea Party is reining in federal spending commitments. Not all Republicans can be counted on to do this once in office.

Even when Republicans hold power, the federal government tends to grow in size and scope. The best recent example of this was when George W. Bush was president. For most of 2001 to 2006, Republicans also controlled Congress. For the last two years of this period, they enjoyed a 55 to 45 majority in the Senate.

Discretionary spending grew faster than when congressional Republicans shared power with Bill Clinton in the 1990s, even adjusting for post-9/11 homeland security expenditures. The budget surplus gave way to large deficits. A new entitlement and a new Cabinet-level department were created.

Conservatives have historically been selective in their primary challenges. Only the most liberal Republicans — Edward Brooke, Clifford Case, Jacob Javits, Arlen Specter — drew credible opponents. Despite imposing wage and price controls, Richard Nixon's conservative primary opposition was limited to John Ashbrook.

In recent years, though, conservatives have changed their approach. Why nominate someone who would earn a 70 percent American Conservative Union rating when you could elect someone who would get 90 percent? More importantly, why nominate someone who will compile a conservative voting record when you could get a conservative leader?

Bob Bennett had a conservative voting record while representing Utah in the Senate. Trey Grayson probably would have had one representing Kentucky. Mike Lee and Rand Paul, however, are conservative thought leaders and Senate boat-rockers.

It sounds smart, right? But this strategy for shrinking government has run into unanticipated obstacles. Not every conservative candidate is of Lee's or Paul's quality. Not every state is as conservative as Ted Cruz's Texas. Conservatives who can't get elected, or who can't govern once in office, can't cut government effectively.

The dilemma: Do you vote for Mike Castle, who was unreliable but surely would have become a senator in 2010? Or Christine O'Donnell, who was conservative but had no hope?

Worse, just as the Republican establishment once paid lip service to conservative concerns in exchange for donations and votes, Tea Party groups are under fire for doing much the same thing. They set unrealistic expectations for the base and then fundraise off the Right's anger and disappointment when Republicans fail to meet them.

Going back to indiscriminately supporting Republicans no matter how uninterested they are in conservative policy goals is sure to disappoint. But so is tilting at windmills.

Conservative primary challenges have helped nudge the GOP's center of gravity to the right even when they fail. But lawmakers who vote right are not necessarily the same thing as lawmakers who achieve the right results.