Of the two candidates, Obama has taken the clearer stance on the issue. He generally supports the Democratic-led House Judiciary Committee in its effort to subpoena the White House, even if it means — as president — he might be weaker for it.
"This blanket notion that you can't subpoena White House aides where there's evidence of genuine wrongdoing I think is completely misguided," Obama told reporters recently. "We're a nation of laws and not men and women so, you know, and that's a precedent I don't mind living with as president of the United States."
He did add the caveat that, "if there are specific assertions of executive privilege, then you know those can be examined."
In other words, White House aides can be subpoenaed, but the president has a little wiggle room.