When lawyers try a criminal case in America they are very alert to what their opponent says and does  since, overwhelmingly, what your opponent says and does is designed to hurt you. It's very much a zero-sum game.

Russia's thinking re Syria is also zero-sum. The US is Russia's enemy, the US is anti-Assad, therefore it is in Russia's interest to be pro-Assad.

Not everything one lawyer does in a criminal trial hurts the other lawyer's case. You don't have to be very experienced to realize that objecting too much annoys the judge and the jury.

And then there's this. Sometimes one trial lawyer is really good. Good trial lawyers know how to plant credible disinformation in the opponent's mind. In some rare instances a really good trial lawyer knows his opponent so well and has the credibility and the rapport to actually suggest a strategy, appearing to make a slip, but in reality knowing that the other lawyer's zero-sum thinking will cause him to do the opposite. The good lawyer's advice really is in the less-good lawyer's interest to do. But the less-good lawyer thinks in zero-sum terms and so does the opposite. Occasionally, criminal trials turn on such things.