If the Senate trial fails to convict, he couldn't claim double jeopardy as that trial is not related to due process in the criminal justice system, but it would be grist to the mill of Trump and his supporters in the event of a criminal trial. I agree with gillymor about having the courage to go for him fully, but there will be consequences: it keeps him prominently in the public eye for a protracted period - think of the headlines week after week - and it would very likely whip up whatever supporters he would still have by then. I suspect it would still be tens of millions.