Despite having 14 candidates so far for the nomination, the Republican Party is suffering from a dangerous lack of credible presidential hopefuls. More people are declaring every month, just joined by the bombastic New Jersey Governor Chris Christie, which is a new low as the flamboyant national figure of four years ago has given way to a governor mired in economic failure and local scandal.

It is hard to remember that in the last primaries, senior Republicans were pleading Christie to stand against Mitt Romney. The only candidate who is even less acceptable to Republican voters is Donald J. Trump, the property tycoon who has become a self-promoting reality television star with very little political vision. Even the creationist Mick Huckabee and the semi-independent Rand Paul have more support.

The Republicans are suffering from years of Tea Party activists driving out the more mainstream politicians, leaving the extremists in place. This has allowed plain eccentrics like Christie or Trump to achieve a much higher impact than they would have done in a more normal Republican field.

The serious politicians who have come through so far and have to be the front-runners include the mainstream Jeb Bush, the conservative Scott Walker and the dynamic Marco Rubio, who is probably leading the field as his Cuban ancestry allows him to appeal to the important Hispanic vote and his youth and dynamism take him well ahead. He also has the advantage against one of his competitors that he does not have to explain — that he is neither his brother nor father, which will help him keep his message on track.

There is a real danger that this profusion of narrow isolationists will drag the Republicans away from mainstream politics, as can be seen by the partisan tone of the attacks on President Barack Obama’s deal with Iran. Any party preparing for power needs to be able to use it for the wider good rather than pander to its special interests.