It appears that several presidential candidates would like to put American boots on the ground in Iraq and Syria to destroy the Islamic State. Here are two relevant quotes about the Vietnam War to bear in mind:
The Vietnamese, had we bombed them to the stone age, would have gone back into the jungle, waited us out. They knew something that we also knew but didn’t acknowledge and that was that someday we would go home and they could come back and rebuild what we had destroyed.
– James Thomson, Jr., National Security Council staff member under Lyndon Johnson
I think I have made two mistakes in judgment. One was that I underestimated the tenacity of the North Vietnamese. And I think I overestimated the patience of the American people.
– Dean Rusk, Secretary of State, 1961-1969