It's a decision that is clearly the most difficult of Barack Obama's young presidency -- whether to heed the pleas of top military officials to send more troops to Afghanistan in a conflict some fear could become his Vietnam.

The president's dilemma has drawn parallels to Lyndon Johnson's deliberations about Vietnam 45 years ago as Obama grows noticeably thinner and confesses to skipping meals as he ponders the risks of escalating the United States presence in Afghanistan.

Like Johnson, Obama came to power with an ambitious domestic agenda as a controversial war raged overseas. His presidency hasn't yet been hijacked by an enormous American casualty rate in a faraway land against a stealthy enemy, but his closest advisers worry that it could be.

"The lesson of Vietnam surely is how can you get a nation engaged in it? It seems hard to imagine that Afghanistan is ever going to be a popular war," said Stephen Hess, who worked for Richard Nixon as the Republican president dealt with "Johnson's war" after his 1968 election.