Headline writers keep paraphrasing him like that, but let's look at the quote:
“Well, you know, the truth of the matter is that as President of the United States, I’ve got a lot of responsibilities. Uh, I was supportive of Tom and, uh, have been supportive of Tom. Uh, obviously, uh, you know, I would have loved to have seen a different result."
He doesn't say that he didn't go because he's "got a lot of responsibilities." I'll accept that "I've got a lot of responsibilities" is pretty close to "I'm busy" (but not exactly the same, because you could have a lot of responsibilities and do them efficiently and quickly, and you could also be failing to meet your responsibilities).
What I'm not seeing is an assertion that being busy was the reason for staying out of Wisconsin. After the bland expression of support for Tom Barrett, the next line is not "I would have loved to have visited Wisconsin for the campaign." It's "I would have loved to have seen a different result." That subtly accommodates what we suspect was real reason for staying out of Wisconsin: He knew the result was going to be a Barrett loss and he was sorry about that and unable to change it.
Watch the clip. It does sound weak and pathetic, but I think it's incorrect to make it seem as though he didn't care enough or want to bother with Wisconsin. I think you can tell that he's really sad about what happened, and he feels — and felt — powerless to affect it. This man is not projecting the energy and confidence he should have at this point in his campaign.