Today the Tea Party returns to the fore as challenger Richard Mourdock prepares to unseat 36-year incumbent Sen. Dick Lugar in the Republican primary in Indiana. In Wisconsin, Democrats head to the polls to select the candidate who will challenge Republican Gov. Scott Walker in next month’s recall election–and the unions’ favored candidate is fading, as are arguments against Walker’s collective bargaining reforms.

Already, the Tea Party had been written off as an electoral force by pundits who saw grassroots conservatives struggle to unite around a single presidential candidate in the Republican primary, while Gov. Mitt Romney–strongly opposed by some Tea Party members–emerged as the GOP nominee. However, the Tea Party continues to drive the agenda on key issues where its positions resonate with those of the general public.

In Indiana, the salient issue is the perceived corrupting influence of long-term incumbency, and of Washington, D.C., where Sen. Lugar has spent the better part of four decades, struggling to maintain residence in his home state. In Wisconsin, the defining issue of collective bargaining reforms, which divided the state a year ago, is becoming a point of consensus as voters note the savings–as well as the layoffs avoided.

It remains to be seen whether, and how, the Tea Party will be a force in the general election–not just in the presidential contest, but in the fight for control of Congress. Several Tea Party freshmen in the House of Representatives are vulnerable, and the GOP establishment fears that an opportunity to take the Senate could be lost (as it was in 2010) if Tea Party candidates cannot defeat their Democratic rivals in November.

Regardless, today is a sign that on the issues, and on the ground, the Tea Party is as strong as ever.

Update: In other closely-watched primary votes, North Carolina voters will decide whether the state should adopt a constitutional ban on same-sex marriage. Former President Bill Clinton has been sending robocalls to voters in the state urging them to defeat the measure–ironically, since it was an election-year Clinton who signed the Defense of Marriage Act into law in 1996.