My view on this as an outsider, given the news we got about the recent economical crisis the US is in, the only way I can see it, is it being some sort of 'publicity stunt' from McCain.
Yesterday on the news I heard that he did not take a real statement about the rescue plan (if anybody could explain to me what this really is, I would be obliged) and since a lot of people world wide and I think also in the US itself, hold the government Bush responsible for the crisis, it would be wise to take a statement and defend it while he was there.
On the same news show I also heard that even the Republicans were not happy with his visit to, I believe it was DC. Should he have made a good statement, and good arguments to defend or kill the rescue plan and bring it on television he could have won voters. Right now he only lost them I think.