The race for future control of the U.S. Senate comes down to a simple question: Will the bulkhead of incumbency withstand the wave of change? As good a test case as any is the race of Sen. Mary Landrieu (D-La.), whose opening television ad is a classic case of how an incumbent runs scared.  In the spot, produced by Democratic ad maker Mark Putnam, Landrieu portrays herself as a tireless advocate for Louisiana’s interests, points out her repeated challenges to President Obama and notes that she has recently assumed chairmanship of the Senate’s Energy and Natural Resources Committee, a key position of advocacy for her gas- and oil-producing state.

The spot is a classic of the genre of incumbency advertising, but is also more subtle and powerful than many of its type. The visuals firmly root Landrieu in the living rooms and workplaces of working people; they (and we) see the senator in a series of newscasts fighting for her state, which give her claims greater credibility than the tired format of testimonials or straight voiceover.

But despite this ad’s effectiveness, with many more to follow, it isn’t clear whether Landrieu and other Democratic incumbents will be able to triumph over voters’ punishing mood. Wave elections see voters act out their anger in seemingly irrational ways. In less volatile years, the chairmanship of a key committee would be seen as a strong reason for reelection; in wave years, voters’ desire for revenge sweeps it away.

2014 reminds me of 1994, when Democrats ended up losing the Senate.  That year I was working for several incumbent senators’ reelection campaigns, including Jim Sasser’s campaign in Tennessee. Sasser, who was running for his fourth term, was the favorite to be elected majority leader if the Democrats, as was assumed, retained their majority. His opponent was a wealthy unknown: Bill Frist, who, in a twist of political fate, went on to become majority leader in a Republican Senate. Frist sailed to victory on a gale of anti-Clinton, anti-Washington fervor, expressed here in another classic of the political ad genre, the anti-incumbent spot, run not by Frist, but by Fred Thompson, another candidate for the U.S. Senate from Tennessee. (Due to Al Gore’s election as vice president, Tennessee had two U.S. Senate elections that year.)

In the months ahead, I’ll keep an eye on the Louisiana race as a bellwether for the battle for the Senate. This is a year when incumbents have to rediscover their roots as challengers. So far, Landrieu is doing a good job of summoning her insurgent side.