Good questions, Lulu. To some extent the Dems are (not without reason) a bit hypersensitive on this issue.
For another, they reflexively use any attempt to attack the President. This includes when speaking in a non-partisan matter as head of state. The "politics stops at the water's edge" concept became obsolete quite some time ago.
Perhaps the Democrats assumed that by attacking Bush for supposedly amining his remarks at certain Democrats (of which, to read the text of his speech, there is absolutely zero evidence), they might get McCain to support the President - which he quite rightly has done. They want desperately to paint McCain as a Bush clone.
I think in this case they have overreached a bit, and are likely to start backtracking in the next day or two.
MWL