I’ve read a few biographies of Lincoln and his personal and public letters. In summary, I’m unaware of any major such donations and don’t believe any occurred.

Elections and campaigning were very different back then. It was below the dignity of the office for a President to be directly involved in his re-election campaign. In 1864, there were no public debates, advertising, or campaign. The platform was so starkly different between the Democrats and the Republicans / Union Party that no debates were needed anyway.

With the 1860 election, Lincoln travelled around the country on his own dime and gave a dozen or so speeches. That was it. No advertising. No lobbies. No lawyers. It wasn’t an expensive affair at all.

Lincoln was a very well paid lawyer in Illinois before being elected so he was able to support himself fine. He wasn’t rich but lived very modestly and was totally self sufficient.

The income of the President was quite generous at the time and would have covered any further expense he needed in the next campaign.

If you are looking for some sort of corruption, what was very common back then and which Lincoln partook in was jobs for votes. If a very influential man in a city would vote a certain way or get his supporters to vote a certain way, he could get a good paying federal job.