The first thing that you can always discard is the official stated aim of any US military intervention. When you are already powerful, you do not need to win wars, you just need them to continue as long as necessary to ensure that no one else can develop enough to ever resist you.
If you think that the US lost in Afghanistan and Iraq, just look at Afghanistan and Iraq today, and look at the US. If you think the US lost in Vietnam, look at the situation of Vietnam for the last 30 years versus the situation in the US. If you think the US lost because it did not achieve the stated aim, it is your mistake to believe the stated aim in the first place. The aim is one and one alone; destruction.
If US soldiers die, do you think it matters? There is no compulsory military service in the US. The soldiers are disproportionately drawn from the underclasses; the poor and ethnic minorities. They are from the segment of the population that the power structure already regards as superfluous. If they were not in the army, they would be either dead or in jail, because the powerful want to be rid of them anyway.