Sadly, you're right when it comes to American Jews these days. The rift between American and Israeli Jews is actually a big problem in the Jewish world right now. A lot of leftist American Jews don't even support the state of Israel.
But I would add that the connection between Israel and the U.S. is different than other countries, if only because of the complex relationship between Western civilization the Jewish state (which was founded by Herzl, an assimilated European Jew). The historical influence goes both ways.
I think you have a point that Israelis also recognize Trump as a true political ally. However, I do think there would be a certain level of support even if the US stuck purely to itself due to the shared values of Western civilization and Judaism.
Regarding your second question, I had to look it up. Wikipedia says 10% are orthodox and 18% are conservative (half-orthodox, so to speak). However, these are also the groups that have the most kids while the intermarriage rate for secular Jews is upwards of 50%. In other words, the demographics could quickly change.
Depends which Jews. Jews in Israel are generally pro-Trump, probably because they know from experience what it means to have your own country and fight for it. With Jews in America it depends on how much Torah is in their life. Orthodox Jews overwhelming support Trump while secular/reform Jews seem to have replaced their Judaism with SJW ideology.
Except the U.S. and western European countries share something in common called Western civilization. Israel shares it to some degree as well and therefore we are allies against foreign civilizations (China, Islam,...).