Why Is Pakistan More Legitimate than Israel?
Whenever I have received a call from a listener to my radio show challenging Israel’s legitimacy, I have asked these people if they ever called a radio show to challenge any other country’s legitimacy. In particular, I ask, have they ever questioned the legitimacy of Pakistan? The answer, of course, is always “no.” In fact, no caller ever understood why I even mentioned Pakistan. There are two reasons for this. First, of all the 200-plus countries in the world, only Israel’s legitimacy is challenged. So mentioning any other country seems strange to a caller.... Ref. Source 5
The U.S. Supreme Court struck down part of a federal statute that allowed Americans born in Jerusalem to list Israel as the place of birth on their passport.
The decision is a victory for the executive branch and affirms that "The power to recognize foreign states and governments and their territorial bounds is exclusive to the presidency." Ref. CNN
In answer to the original question - there are many influential Jews living in the USA. Mix that together with religious zealots who want to 'protect' Christ's birthplace and you have enough support to put an American hand over there.
U.S. $38B military aid package to Israel sends message to adversaries
The United States agreed Wednesday to provide Israel a record $3.8 billion a year in new military aid over the next decade. The pact is a sign of the two nations' close alliance despite major differences over Iran's nuclear program and other policies. Ref. USAToday.
Most Democrats consider Israel is 'a burden' on US:
While a majority of Americans (57%) said they would like President-elect Donald Trump to be an impartial mediator between Israel and the Palestinians, 57% also said they believed Trump would lean towards Israel in any negotiations. Ref. Source 2f.