WASHINGTON (AP) -- Barack Obama's two years in the Senate have taken him around the world, from Russia to Iraq to Kenya -- an itinerary more costly to taxpayers than any other senator who took office with him.

The Illinois Democrat's travels in 2005 and 2006 cost taxpayers nearly $28,000 as he studied nuclear proliferation, AIDS, Middle Eastern violence and more.

Eight other freshmen senators took office in 2005, and about $19,200 was the most anyone spent for government-paid travel, according to reports filed with the Senate Office of Public Records.

Obama's journeys are unusual for such a junior senator, but not for someone thinking of a presidential run someday.

"Valuable or not, it's the thing they all do to show that they're knowledgeable about the world," said Stephen Hess, a George Washington University professor and former presidential aide.

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