There are any number of sources online which make it quite clear which laws he has broken. This extract from a piece from Forbes (written before the verdict was given) is a good example.
To claim there is no legal basis for prosecuting him (and now finding him guilty) is just not true.
You might choose to disagree with the verdict but there are laws and he is not above them.
“Trump was accused of falsifying reimbursement checks he paid to ex-attorney Michael Cohen, after Cohen paid adult film star Stormy Daniels $130,000 before the 2016 election to cover up allegations of an affair—with prosecutors arguing the checks were falsely labeled as being for legal services.
While falsification of business records only requires someone to have “[made] or [caused] a false entry in the business records of an enterprise” under New York law, the crime is just a misdemeanor at that stage, and becomes a felony if it’s proven the defendant falsified records “with intent to defraud that includes an intent to commit another crime or to aid or conceal the commission thereof.”
That means the jury must show Trump falsified records to cover a second crime, which prosecutors allege is New York’s election law prohibiting “conspir[ing] to promote or prevent the election of any person to a public office by unlawful means”—since Cohen allegedly paid off Daniels in order to boost Trump’s chances in the 2016 election.
Since that law requires defendants to have influenced an election through “unlawful means,” jurors will also have to determine whether a third crime was committed that made the hush money scheme violate the election law.”