It's nearly impossible to defeat a homegrown guerrilla insurgency who are fighting to preserve and protect their own home land. Invasion troops don't have the same sort of heart and passion for the fight as those who are facing extermination.
As we saw in Iraq, Vietnam, and even in the American Revolution, superior firepower, technology, troop numbers, and logistical support, don't always result in victory. In fact, they almost never do, unless they're set against similar forces.
There's just something powerful about having truth and right on your side in a fight. The majority of the American people have that. The deep left who have infiltrated and usurped our government, don't.