By Major Garrett

A top adviser to Sen. Joe Biden is accompanying Barack Obama on his high-profile trip to Afghanistan and Iraq, raising questions about whether the Delaware Democrat is being considered as a running mate.

Tony Blinken, chief of staff for the Senate Foreign Relations Committee, was accompanying Obama as he arrived Saturday in Afghanistan, committee spokeswoman Elizabeth Alexander confirmed. Biden is the chairman of that committee and Blinken is considered his closest adviser.

Alexander described Blinken's role as standard operating procedure.

"Tony is traveling in his capacity as staff director of the Senate Foreign Relations Committee," Alexander said. "Two of the three senators (on the trip) are on the committee and there is precedent for committee staff traveling with members other than the chairman."

Obama is traveling with Sens. Jack Reed, D-R.I., and Chuck Hagel, R-Neb, whose presence also fueled VP speculation.

Obama, Reed and Hagel were each allowed to bring one staffer on the trip to Afghanistan and Iraq. Hagel, like Obama, is a member of the Foreign Relations Committee.

But Blinken was the only additional staffer authorized to make the trip, giving Biden unique access to Obama's briefings and observations on the trip to both war zones.

The former presidential candidate has often been mentioned as a possible running mate for Obama and his top staffer's presence is sure add to the speculation.

Biden has taken on an increasingly visible role as a surrogate for Obama and went out of his way this week to defend Obama's failure to hold a Foreign Relations subcommittee hearing on Afghanistan and the NATO-led effort there to battle the Taliban and its Al Qaeda allies. Obama had the power to convene such a hearing but did not while he was pursuing the nomination for the presidency.

When Biden ran for the nomination he called Obama's call in August 2007 for two more combat brigades in Afghanistan a "johnny-come-lately" position. Biden now defends Obama staunchly on all foreign policy matters and is viewed, if not as a running mate, then as a potential secretary of state in an Obama administration.

This is Obama's first-ever trip to Afghanistan and Blinken, a former national security staffer in the Clinton White House, could provide valuable expertise, in addition to keeping tabs on things for Biden.