Last month, when Senate Minority Leader Mitch McConnell, R-Ky., cruised to victory in his Senate primary, it was all the rage to declare the Tea Party dead. At the time, I noted that in reality, the Tea Party had only knocked off a few Republican incumbents since it rose to prominence in the 2010 elections.

With the news that Chris McDaniel has forced a runoff against Sen. Thad Cochran, R-Miss., that McDaniel is likely to win, now the political media are saying that perhaps the Tea Party isn't quite dead after all.

Here’s the thing to keep in mind. The Tea Party doesn’t necessarily need to knock off every incumbent to continue to have influence. In reality, what’s important for the movement is that it defeats or seriously challenges incumbents at least on occasion. In their ideal scenario, Tea Party groups would regularly defeat incumbents and have most Republican senators come from within the movement. But the secondary – and more realistic scenario – is to put enough of a scare into incumbents so that they're more likely to cast votes for limited government in office.

Traditionally, it was simply taken for granted that an incumbent senator would be handed the Republican nomination on a silver platter when choosing to run for re-election, and no challengers really had much of a chance. There was a pretty easy path to keeping one’s seat in the primary. A Republican senator could vote to expand government and break away from limited government principles and he’d be likely to regain the nomination if he brought enough money back to the state and kept big business interests happy.

But as my colleague Tim Carney has noted, the emergence of the Tea Party and other similarly-minded conservative groups has created an alternate fundraising path for challengers like McDaniel by tapping small dollar donations from grassroots conservatives. As a result, incumbents cannot take their nominations or rely on the old easy path to the nomination. Sen. Orrin Hatch of Utah is a perfect example of a Republican incumbent who had to move his voting record rightward in order to fend off a challenge.

Candidates like McDaniel don’t have to win every race. But as long as a Tea Party candidate can win – or mount a strong challenge – every so often, then incumbent Republicans have to look over their shoulders and vote more conservatively than they otherwise would have. The Tea Party won't be dead until there are several consecutive election cycles in which incumbents aren't seriously challenged.