in 2004 Bush was already the President, the backdrop could have been a type of replica of the White House...perfectly acceptable for a sitting President.
Obama’s mistake is the presumption of importance...he’s a nominee.
That being said, I agree with other posters who have said i’ts meant to replicate the Lincoln Memorial on the anniversary of the day MLK gave his I Have a Dream speech from the steps of the Lincoln Memorial.
Interesting point, but I still like this:
it was also at the same venue, not at another location specifically for the canidate