Why isn't former President Bush out stumping for his son?Does this indicate a lack of support? Good questions
Now, it could indicate a lot of things. For one, considering the policies of President George W. Bush and the policies of President George HW Bush it is possible that the President's Father has issues with the current President and can't bring himself to support him, even though he is his son.
However, another possibility is that President George HW Bush wrote off politics all together on purpose, simple because he was tired of it. I always wondered why the 41st president ran such a lack luster campaign for re-election. Even if he ran an all-out top notch campaign, he still might have lost to the future 42nd President, however his campaigns performance did not even rise to the level of his first campaign for the office.
About 6 months or so after he left the Whitehouse, I saw him on TV interviewed at home, sitting by the pool. He was relaxed, smiling and in very cheery spirits. When asked what it was like not being the President any longer, he smiled, a very sincere smile IMHO and said he life was wonderful. All this said by a senior citizen in a lounge chair by his pool.
I personally feel that President George HW Bush was glad to get out of politics, and wanted to be out of it to the point of letting his campaign faulter. I think the only reason he was at the convention in 2000 is because it was expected, being he was the last Republican President and his son was running for the office.
The 41st President, as far as I know (but could be wrong) has not been out and about making appearances of doing paid speaking engagements at anywhere near the level of former Presidents. To me this speaks to the man's distaste for politics.
Add to what I think is his hatred of politics, his likely ideological disagreements with his son and I would have been quite surprized if the 41st President was out, actively campaigning for the 43rd.
It doesn't necessarily suggest that the former President considers the current one to be incompetent, or incapable. Just that the former President probably see's the current President as wrong or misguided on several issues.
It is interesting that the Father of George W Bush is not out campaigning for his son, especially considering his stature. But I do not think it rises to the level of scandal or concern. (nor do I feel this was implied by the questions

)