If we don't stop Iran with force, it's Vietnam all over again. The US would be seen as a paper tiger, and every tinpot terrorist would line up to take a potshot at the us. Bush doesn't have a choice -- any finagled 'agreement' with Iran at this point will be seen as a sham. This could all telescope drastically -- if we piddle around much longer and if Israel fails to act, they're gone. We'd have to take off the gloves....but too late for millions of Jews. Not an option Bush or the US could live with.
The war with Iran very likely will weaken USA. As a result it will weaken Israel and Israel will be forced to modify its basic policies in the direction of radical compromise with Muslim neighbors and to established closer relations with the European countries.