Embassies are sovereign territory...since when does the host nation get a veto? since Obama.
Not really; they aren't really totally sovereign territory the way people commonly think they are, though they're customarily treated that way, but even if they were, in the absence of a Star Trek transporter beam, you still have to move anything like more Marines into them
through the host nation's sovereign territory. The Marines themselves do not have full diplomatic status, nor do a lot of the embassy support staff, they have something that's a notch lower.