Republicans know how to use a message to define a presidential campaign. Remember Willie Horton, the ugly insinuation of racial fear by reference to one parole gone awry? I don’t recommend Democrats find their version of this mean message. But I do think they should use one emblematic person and incident to define their distinctive message in the present campaign.

Lilly Ledbetter, the woman from Alabama who was treated unfairly by her corporate employer — Goodyear Tire and Rubber Company — sued and won for economic discrimination based on sex, is the person and the message. The United States Supreme Court overruled her lower-court victory because she hadn’t sued on time, though she did bring her case when she discovered the discrimination. Lilly Ledbetter is the metaphor for those hardworking women with limited education and modest wages whom Hillary Clinton touched in her campaign. Barack Obama needs to reach out to these women; he has reached well-educated women already. Lilly Ledbetter should be on Democratic National Committee and Obama television ads, and with the senator in key appearances in areas where she is a metaphor and where he needs help — Pennsylvania, West Virginia and Ohio, for example.

The two justices John McCain said would be his models for replacements of future seats on the high court voted against Lilly Ledbetter and for the discriminating corporation. Justice Alito wrote the opinion. Sen. Obama, and Sen. Clinton on his behalf, needs to hammer at the importance of federal court, especially Supreme Court, appointments. Lilly Ledbetter’s problem is not the only one women care passionately about — Roe v. Wade is a hot-button issue Democrats and Sen. Obama should embrace; Sen. McCain will for opposite reasons.

Lilly Ledbetter could be the Democrats’ Willie Horton, but she would be a messenger with a decent, high-minded, politically exploitable message.