Quote from Cutten:
French President (by far the most domestically powerful G7 political office), UK and Canadian PMs, the German Chancellor.
A US president with a hostile Congress is a lame duck domestically. Whereas to become PM your party is automatically the majority in a plurality system, and the majority party or biggest coalition party in a proportional representation system. Yes with a large majority in Congress a President is fairly powerful, assuming his party all keep in line, yet a PM is just as powerful with a 1 vote majority on the same assumptions and can't be filibustered. None of the PMs have term limits, and no judiciary is as powerful an obstacle as the US Supreme Court & Constitution. The French President can even dissolve the assembly and suspend the constitution.
Coalition governments are a feature of systems that use proportional representation, but even then some countries (e.g. Japan) have a dominant party almost all the time. And plurality systems like the UK and Canada rarely have coalitions and aren't remotely fractured in nature.
Unlike every other G7 country, if Obama "abrogates contract law" then he will be successfully challenged and lose in the Supreme Court - unless he manages to alter the constitution, or emergency powers are declared, both of which are harder in the US than most other countries.