If there is one thing that horrifies and absolutely tears liberals apart it's Trump achieving another victory. If the killing of the #2 leader in Iran actually leads to the overturning, and fall, of the current Iranian regime just as Reagan's statements led to the eventual fall of the Wall in Berlin, then you can bet on two things happening. They will never give credit to Trump and they will always find some way to spin it as something bad.
Democrats are vested in defeat for anything good for America and are doing all they can to undercut President Trump at every move. Their overt and immediate steps to attempt to limit Trump's powers, specifically with respect to Iran, do more to embolden Iran's regime than anything else. They want to give credit to the Swiss trying to say Iran didn't hit back harder because of efforts of the Swiss to mediate rather than the more likely fears, of Iran's leaders, that any further killing of Americans would lead to the eventual destruction of their own regime.
Now it seems that internal dissent from within Iran seems emboldened and energized by Trump's attack and this very well could lead to the eventual change of leadership within Iran. As I said though you can bet Trump would never get credit.