Nope. It is perfectly legal to donate to any politician at any time, within limits imposed by the law.
If one is strictly operating as a businessman, and if one wants to grow his business, it is not smart to donate to only one stripe of politicians.
But as I explained in a previous post, if one is an elected republican holding office, then it should raise eyebrows if one donates to democrats.
Trump was never a RNC official, an elected republican or a party hack. Until 5 months ago, he was strictly a businessman in the multi-Billion dollar class.
If Trump is found to have donated to democrats AFTER declaring run for political office as republican, that would certainly be un-ethical.
That's not what you posted before. You said, "He gave it so they would not harm his business interests."
Nice place you have here. Be a shame if something happened to it.