That's a good line. It puts him firmly on the side of labor which has to be totally energized for the Kerry campaign to beat the conservative affirmative action of the Electoral College. And it also conveys likable strength, which is one of Bush's main advantages over anyone else.
(But it also indicates Kerry's resume- and record-oriented attitude, as in: Vote for me, because I've been here in D.C. for 18 years and if you read the paper, you know I'd be a good president. I think that's part of why Iowa voters flocked to him, because they liked matching up his record of military service and foreign affairs to Bush's, but I'm not sure that the swing voters in the swing states care so much about resumes and records. I think that stuff plays better among educated people, and college-educated voters are not the deciding factors this year. I saw more of this orientation after his meeting with Nader, when he said something like 'I know you have your differences with Bill Clinton and Al Gore. But I've had a different record in the Senate. I've been with you on these issues.')
Anyway, a nice line.