Since WWII we have "lost" every war we have been in because the American people will not, do not, fight to win, we think nothing of sending someone else kids/fathers/mothers to war as long as it does not interfere with our reality TV shows. We went into Afghanistan halfheartedly with no plan to reconstitute any form of social/governmental direction or control and once we decapitate the existing government, as bad as it was, we drew down and went into Iraq and abandoned our responsibilities in Afghanistan. We have abandoned true international and military knowledge and experience with academic feel good armchair philosophy that has accomplished nothing but getting people killed and maimed. Then we decided that Assad and Qaddafi had to go and we have a major global problem on our hands.
This all occurred under both mainstream Republican and Democratic leadership and everyone's hands are dirty so it is time to stop blaming and find a solution. Given the weak kneed attitude of the American people, any more military intervention in the area either needs to be overwhelming or a withdrawal. Anything else will accomplish nothing.
So, I my view, Trump is right. We started the fight but did not finish it. Either fight to win and fight with overwhelming force, or stay home and change the channel....