Had he declared it to the FEC as a campaign expenditure, then Trump would be in trouble for personal use of campaign funds.
That's only if you buy the lie paying off the women to keep silent had nothing to do with the campaign. Which is absurd. When were these two affairs? A decade ago yet somehow there was a need to keep them silent just before the election?
But if that's not enough for you, Cohen recorded his conversation about the expenses with Trump where they conspired to avoid FEC regulations.
As for use of campaign funds, the money came from the Trump Foundation, so charity fraud even if there were no FEC violations.
Here's the thing more than a few people keep missing even though it has been spelled out:
There was no legal offense in using campaign money to pay the women off
if it had been reported, which it wasn't. So if it was a campaign expense, they failed to report it.
The offense was in the fact the money was an undeclared campaign donation. If the money came from Cohen, it was a campaign loan, needed to be declared.
If the money came from Trump, there are limits in personal donations to one's campaign as well and it needed to be reported. And the fact Trump ordered his kids to use the Trump Foundation money to pay Cohen back, that's also a crime.