Some of the isolationists are really against anyone who is not like them. America has this strong tradition from the time of country founding, when US tried to not get involved into endless wars between European powers. It served the country well and helped it develop while others were busy destroying each other. Until the time US became so strong that it became a moral issue where US is capable of changing the world to the better. This struggle happened in both WW1 and WW2, where US was not prepared militarily (Army was almost non-existent) but very capable due to industrial strength. (Btw, those who criticize FDR for not intervening enough on behalf of Jews, should also give him credit for pushing USA into the war despite strong opposition).
Republican party in 20th century had a sizeable isolationist minority (see Pat Buchanan, for example), and now Trump brought more of amei haaretz who used to be democrats (“uneducated” that he loves). Without this realignment, same amei haaretz would be joint with anti-Israeli left with way more damage. So, we need to recognize that democratic reality and try to work with or around them. Bibi did this brilliantly – by cleaning the path for B-2s from air defense and letting Trump take front stage with a spectacular makeh b’patish, allowing T to take credit but also claim that involvement is one-time only. As Chofetz Chaim sid – in uor times, one need to be klug, klug, and then frum.