An old argument against Proportional Representation was that PR would allow extremists and Nazis to get elected. With Trump’s election that should be dead. One of the USA’s two main political parties now has denying voters that they suspect of being likely to vote for the other party as its main electoral strategy. It has relied on gerrymandering up till now to keep control of the House of Representatives. While the size of the popular vote for Democrats was large enough, this time, to overcome gerrymandering, Republicans, solely through gerrymandering, continue to control the assemblies of many states, despite losing the popular vote. On issues such as gun control and health care the Republican hold positions that in a normal democracy would place them in the lunatic fringe of the hard right. If you want to find an equivalent to the British Conservative Party don’t look for it in the Republican Party - look for it on the right of the Democratic Party. First Past the Post does make it almost impossible for extremists to get elected but the two party monopoly that it produces makes political systems that rely on it uniquely vulnerable should one party of the duopoly be captured by an extremist movement. That the Democratic Party draws support from everyone from socialists like newly elected Alexandria Ocasio-Cortez to conservatives like David Frum is not a strength - no party can meaningfully bridge such a wide divide. Sadly, simply being the party of sane people is not a platform and hence it is the more focused Republicans that control two and half of the USA’s three branches of government. In Britain, Theresa May with her deep hostility to immigrants represents a huge step from the traditional conservatism of David Cameron towards that of today’s Republicans but the real danger is that Brexit will open up to extremist capture in the form Rees-Mogg. In normal times Rees-Mogg would fail to survive the vote of Conservative MPs to be one of the two candidates put to the party membership. But these are not normal times and he would be a strong favorite in any contest among the membership. As leader of the Conservatives Rees-Mogg would have the majority of British voters against him. But with the electorate divided between Labour, Lib-Dems, Greens and nationalists he wouldn’t need a majority - thanks to First Past the Post. Proportional Representation does reduce the initial barrier to extremist parties but allows the sane parties to better oppose the extremists because they are not forced in an unnatural unity. The Achilles heel of First Past the Post is extremist capture of one of the two main parties and that danger should put Proportional Representation on the agenda of both Britain and the US.