As a foreigner (French) I'm surprised that Americans apparently don't get that mixing a career in politic with a career in justice is the open door to abuse, demagogy or conflicts of interests. This should not be allowed or even possible.

We understand it some. It is very, very rare for a judge to join the legislative or executive branches. I can't think of an example at all.

However, people moving between legislative and executive branches of the government is pretty common. State legislators become governors, governors become federal legislators, federal legislators run for president.

In the US, prosecutors are part of the executive branch. That's because their job is to represent the state. They are supposed to seek justice, but in the context of an adversarial system. Judges are nominally neutral umpires; prosecutors battle with defense attorneys. Both sorts of attorneys are expected to fight vigorously but fairly for their side. So the burden of fairness mainly falls on the system and the judges, not the partisans on either side.

But yes, that does produce a conflict of interest when deciding what crimes to prosecute. They have an incentive to pick cases that benefit both the state and themselves.

It is indeed very different than the rest of the world. In US, not only careers in politics and judicial system often mix, but often career in the judicial system IS career in politics directly. Many of the high level positions, district attorneys, judges (not federal) are elected positions, hence by definition political.

Note that the UK government is currently in the process of adopting such policies. If they're successful, look for this sort of arrangement to be proposed in other European countries as "reforms".

I didn't like the sound of that when I first heard about it. Now I am dead set against it. Politics and the justice system have no business being connected like this in any way.

The system is so horribly compromised in the US it's hard to see how it can be meaningfully fixed. What a mess.