To Americans of a certain age, the conflict in Afghanistan is beginning to look a lot like the Vietnam War. There are crucial differences, however, and they need to be borne in mind.

U.S. troops continued to fight — and die — in Vietnam long after Washington stopped trying to win that war. The long, bloody pullout can be blamed on public opinion that turned against our involvement.

Reports from Afghanistan are beginning to sound like those during the last few years of the Vietnam War. Taliban terrorists are gaining ground. Some Afghan government forces are battling them valiantly, but others are giving up the fight, sometimes cooperating passively with the Taliban. In some areas, it appears U.S. troops and bombing raids are all that are preventing a collapse.

Taliban leaders began smelling victory when former President Barack Obama started pulling U.S. troops out of Afghanistan. Now, President Donald Trump has said it may be time to cut our losses and get out of the conflict entirely.

And many in the public seem to be weary of the war and its cost to America in both blood and money — though antiwar sentiment is nowhere near what it was in the late 1960s and early 1970s.

We know for a fact that the Taliban hosted al-Qaida terrorists prior to the Sept. 11, 2001, attacks on America. If they regain power in Afghanistan, will they once again become a haven for vicious Islamic fanatics? That simply must not be permitted.

If Trump and other U.S. leaders decide on a complete pullout, Taliban commanders must be convinced that renouncing support of terrorism is in the best interests. Similarly, it needs to be impressed upon them that the truly evil policies of their former reign cannot be resumed. In some convincing fashion, the Taliban need to be made to understand that a sharp red line exits between acceptable behavior and that which will prompt crushing U.S. retaliation.