Originally Answered: Is Barack's credo."The Buck stops.with Bush" Take Afghanistan-isn't Barack expanding the war, not Bush?
Given the additional detail you added, are you saying "Bush started it" is irrelevant? Please put your partisan political feelings aside; they have nothing to do with the reality, and anyone who thinks so becomes the real blind mouse. (In a parallel example provided below, Vietnam, it was the Democrats that started it, and the succeeding Republicans took necessary steps in what proved to be an unpopular war; the second Republican, Ford, only made the decision to leave when there was simply no other choice.)
Even if Afghanistan lacked justification, as in the case of Iraq, it is not unusual for a president to clean up the mess made by a former president. Take for example, Vietnam. I believe JFK wanted to give France a hand initially by sending in a token force, and then (after France bowed out and the U.S. was left holding the cards) his successor (LBJ) expanded the war greatly, while the next successor (Nixon) went even crazier, going so far as to bomb a neighboring country -- all for a war we had no business in, in the first place; but as the years went by, reasons connected to the realities of the Cold War grew, the danger of the Domino Effect got out of hand, and then the U.S. had to "stay the course" once so much investment had been made, and the chance for winning was still viable.
In short, a newly elected president can't afford to enact policies created from a position of isolation. A president needs to consider the status quo that has been created even from reasons the president might have been opposed to. In short, a president has the responsibility to preserve the honor of the United States, given the steps, or missteps, his predecessor might have made.
The decision was (rightly) made to go into Afghanistan to chase the perpetrators who attacked the USA. The USA succeeded in toppling the government that was helping the group responsible for 9/11, and then what? Once there was "Mission Accomplished" (as Pres. Bush said about Iraq) in getting rid of the Taliban, the U.S. couldn't simply pack and leave. There was a great void in the Afghan government, and there were all those agreements made with the tribal chiefs that made the mission in Afghanistan initially successful. But then what? Given the combination of misguided efforts by the U.S. government (trying to force a Jeffersonian democracy on a culture far from ready for it), as well as corrupt leading forces in Afghanistan (controlling both the weak central government and the outlying provinces, governed by individual, greedy warlords), a powder keg was set in place. And as the U.S.'s attention stupidly wandered into another foreign adventure, whatever gains that were made in Afghanistan were diminished over time, what with the anti-U.S. propaganda that was instilled in the local population, allowing the Taliban and Al Qaeda to consolidate and re-grow.
What is the way out of this situation -- to diminish the forces, as the U.S. position grew weaker? Obviously not; that would defeat the original purpose (especially if the original purpose, unlike the case of Iraq, was a sound one.) And if the U.S. cuts and runs, a far more dangerous setting will have been created with probable future ramifications against U.S. interests.
The case to leave is stronger in Iraq, a country the U.S. had no business in, in the first place. But what do you call a superior power that goes into a poor country, wrecks much of the infrastructure, allows museums to get sacked, kills hundreds of thousands of innocent civilians, and then leaves after the villainous leader is caught and executed and a relatively powerless puppet government is established on paper? Where such violent interference has rocked the security and sensitive interrelationships of the nation, with once-unified groups (Shiites, Sunnis, Kurds) now often at each other's throats -- with car bombs going off every other day?
You would call such a nation highly immoral. If you cause destruction, it becomes your duty to clean up the destruction, especially when enough historical lessons have been observed through the generations, when the USA learned the high price that comes with not rebuilding -- when the demon is allowed to leave the bottle, and is allowed afterwards to roam unchecked. Decisions involving great power carry over into great responsibility -- and while someone like Obama may not have approved of his predecessor's actions, it is his duty to clean it up. (U.S. policy in prior existence cannot be kept separate from the newcomer's general mode of thinking, and must be acknowledged; a president must preserve the honor and responsibilities of the country he has sworn to serve, in cases where previous decisions have serious carry-over effects, even when the duty is not to the liking of many of its people.) It is ridiculous for those to blame Obama over the consequences of these two wars, as though his presidency took place in a vacuum, and the world we live in is uncomplicated.