Yes there is a Jewish lobby, just as there are lobby groups for every single organization on the face of the planet, from tobacco, to atheists, to the Vatican! They arent always representative of the people they claim to represent, b/c they arent elected and what not, and are considered non-governmental. But lets not conflate that with a Holocaust conspiracy, or a nefarious Jewish plot to rule the world!
Holocausts notwithstanding, if you or others are sceptical of an "Israel Lobby" (which is overwhelming Jewish of course)that is significant well beyond any standard lobbying group, I would highly recommend a read of the book of that same name,(nearly all of it is available in research paper form online)or officially, "The Israel Lobby and U.S. Foreign policy," by John Mearsheimer and Stephen Walt. These are no "neo-nazis" by any stretch of the imagination, and they bend over backward to endlessly attempt to denounce any "conspiracy-theories" regarding Jews directly. But their own work betrays this emphatic denial on many levels. In over 350 meticulously researched and noted pages, they cannot adequately explain why this so-called Israel Lobby is so powerful in the first place - only that they DO have great power. While they sensibly concede that many nations Lobby the US(and other)Government(s)from within for favor, the fact that this Israel Lobby is literally feared in Washington like no other, and crossed at risk of one's political career is as unique as it is astonishing!
In other words, while many Lobbies are present and some powerful, all pale in comparison with Israel, and there is no logical, strategic (politically or logistically speaking)reason why. Thus they make a fantastic case for showing that this Israel Lobby does exist(which many deny out of hand), and that it is indeed very, very influential - but they cannot explain why this Jewish led movement, despite disagreement even between various factions, enjoys this unprecedented power, access, and influence in the first place.
While "conspiracy" in the traditional sense, may indeed be the wrong characterization for this peculiarly, singularly powerful and influential movement, it is then unclear exactly what this entity is; and more importantly, why it exists and thrives in broad daylight, even as its most powerful architects and engineers, and fanatical supporters basically deny it is even there at all. Which is, ironically enough, the very stuff conspracy theories are made of...