Democrats ran anti Romney attack ads for months. They accused Romney of being a vulture capitalist who bought up companies and closed them down, throwing the employees out of work
Romney should have said something like this "At Bain we financed this successful company, that successful company, some other companies, who are employing a fantastic number of workers, full time with benefits." Romney didn't say that, or anything else. He was silent.
And voters like me begin to think the attack ads might be right. If Romney doesn't deny these really awful accusations, maybe they are true.
Rule of thumb, you have to answer attacks. Ignoring attacks doesn't make them go away. Some political "consultants" will say that denying an attack just spreads it. Not true. Lack of a denial hurts Romney, and the democratic newsies will spread it no matter what you do. So deny all attacks. ASAP.
That's not the only reason Romney lost, but it's a big one.
Dukakis could have told him about Willie Horton.