Gerhard Schröder offered a clear German NEIN to an American president's war of aggression that was in violation of international law. That took courage. Ms. Merkel did not join him at the time. If Trump now begins to take the wrecking ball to our set of values, we must say clearly: That is not our approach.

It is impossible to swear an oath to the German Basic Law without realizing that our constitution is among the most liberal constitutions in the world. As the head of government in such a country, I would stand up to all those who call into question this free, open and tolerant model of society.

If we want to defeat Islamic State, we first have to arrive at a cease-fire agreement in Syria. Once that has been achieved, an anti-IS coalition can be assembled, including Russia, Saudi Arabia and Iran. That, however, will be significantly more difficult in the wake of Turkey's downing of the Russian plane.

We agree: Brussels can't regulate everything. I'm driven by something else: There are forces in Europe that want to generally give national policy priority over a common European approach. We have to prevent this.

[Helmut] Kohl said Europe must return to being a community committed to stability and the rule of law.

For German Social Democracy, Europe is vital to the national interest.

At the end of the day, men like Donald Trump need to be given that which they themselves dispense: clear messages. I would confront him as clearly and explicitly as possible. It is not only the right, but also the duty, of the leader of a German government to do that.