Maybe so, but the fact that he and Cohen channelled the money he used to make the illegal payment through Trump's business, and then created false allocation labels for that payment in an attempt to hide what it was, where it came from and where it went, is not just a campaign violation; what they did is money laundering, 18 US Code § 1956, violation of this statute
can resut in prison time.
18 U.S. Code § 1956 - Laundering of monetary instruments
(a)
(1) Whoever, knowing that the property involved in a financial transaction represents the proceeds of some form of unlawful activity, conducts or attempts to conduct such a financial transaction which in fact involves the proceeds of specified unlawful activity—
(A)
(i) with the intent to promote the carrying on of specified unlawful activity; or
(ii) with intent to engage in conduct constituting a violation of section 7201 or 7206 of the Internal Revenue Code of 1986; or
(B) knowing that the transaction is designed in whole or in part—
(i) to conceal or disguise the nature, the location, the source, the ownership, or the control of the proceeds of specified unlawful activity; or(ii) to avoid a transaction reporting requirement under State or Federal law,
shall be sentenced to a fine of not more than $500,000 or twice the value of the property involved in the transaction, whichever is greater, or imprisonment for not more than twenty years, or both. For purposes of this paragraph, a financial transaction shall be considered to be one involving the proceeds of specified unlawful activity if it is part of a set of parallel or dependent transactions, any one of which involves the proceeds of specified unlawful activity, and all of which are part of a single plan or arrangement.
Additionally, the fact that they did this together with the intent to subvert campaign laws could also put them both in violation of RICO statutes.
In any case, the impeachment of a US President does not require that the high crimes and misdemeanours he commits are attractive of punishments involving prison time, they only need to be crimes, and what Cohen and Trump have done here is commit crimes. If Trump was not POTUS right now, he would already have been indicted right alongside Cohen.