In the US an amendment must also be ratified by 75% of the states, usually within a time limit.

IOW the supermajority needed is not two-thirds but three-quarters in some bodies (though isn't it lower in the Senate?), which would make the venture harder. It also helps that the US parliament is bicameral, Hungary's unicameral.

As Berlusconi learned, it is very difficult to change the Italian constitution.

He never had the required super-majority, or did he?

Constitution of Italy - Wikipedia, the free encyclopedia

In order to make it virtually impossible to replace with a dictatorial regime, it is difficult to modify the Constitution; to do so (under Article 138) requires two readings in each House of Parliament and, if the second of these are carried with a simple majority (i.e. 50%+1) rather than two-thirds, a referendum.

_{*Lunatic*, n.
One whose delusions are out of fashion.}

It took slightly more than a year to ratify the 18th amendment. The 23rd took about 10 months, and the 26th took less than 5 months. It's become harder since then: the 27th (and last) took over 2 centuries...

Returning to the US parallel. For Fidesz's two-thirds majority, the key as winning almost every one of the single-member election districts in Hungary's mixed election system. In the US first-past-the-post system, a supermajority in a single election is possible with even smaller majorities. However, it would need the end of the bipartisan system for the situation to arise: either one party would have to alienate the majority of its voters enough to stay away from the vote (as more or less happened in Hungary) or split in two equally strong parts with weak geographical correlation and divide votes (somewhat similarly to the way Thatcher got her crushing election victory while Labour and the SDP-Liberal alliance split votes). Due to the non-simultaneous Senate and gubernatoral elections, most of the time, this situation would have to hold for two years for the other major party to win the supermajority in all three Constitution-relevant bodies. However, checking the current list, I see the half of the currently 20 Democrat governors are up for re-election (or replacement) in 2015. So would there be no shift favouring the Democrats until then and would the above charted extraordinary situation arise in 2014, the Republicans would have the opportunity to gain all the supermajorities in one year, even without winning over a single new swing voter.

_{*Lunatic*, n.
One whose delusions are out of fashion.}