Why would the Senate elected by the same electoral group that elected the House that impeached him be less likely to convict and remove than a Senate elected by the States?
I’ve lived in several states, and in none of them have I seen any reason to believe the legislature would be more likely to elect a good Senate than the general populace. To be fair, part of this is no doubt due to the loss of relevance for the states the 17th Amendment contributed to.
The point was not a "good" senate, whatever that means, but an avenue of federalism whereby the States had a strong voice in Washington to temper an ambitious and abusive central government. Popular vote removed federalism from the national legislature, to the enduring detriment of the States. And ultimately the Nation as a whole.
The change was of course a part of the Progressive Era agenda in the early twentieth century, the most catastrophic 20 years in the nation's history.
The goodness of the men elected or appointed is far less important than their interest, or rather, to whom or what they are responsible.
Today's Senate is just another House of Reps, only more dangerous. The rhetoric and voting pattern of the typical rat Senator is indistinguishable from his siblings in the House. Both houses are perfect breeding grounds for demagogues beholden to the whims of the mob. That is okay in the House, and the Framers expected it. It is called consent of the people.
Our liberties were generally secure as long as a wild House of Reps was countered by a deliberative body that represented the interests of the States.
If not all State Assemblymen are very honest, that's okay from a national standpoint, for they would still be protective of their interests.
Simply put, the 17th Amendment effectively repealed the 10th. It removed the structure necessary to protect it. James Madison was cool toward Bills of Rights not because they were dangerous in themselves, but because he feared we would rely on "parchment barriers" to despotism rather than the structure of our government.
One more example: What right is most closely guarded? Notwithstanding Obama's recent assaults, freedom of the press is unrestricted. It is so not because the 1st Amendment says so. It is because of the self interest of the press that defends it.