Assuming, for the purposes of argument, Trump is impeached by the House and further assuming, also for the purposes of argument, he is acquitted by the Senate, he is likely to do something really, really stupid and dangerous between his trial and the next election. He will be totally convinced of his own invincibility. The Senate would be well served to convict him because once they let him off the hook and he runs off and drops a bomb on someone, literally or figuratively, it's on them forever. I realize they are chicken-shit afraid of his voters, but sweet Jesus.
If the Senate were to vote by secret ballot, like a real jury, I have no doubt Trump would be convicted and removed.