However if He is willing to do that to the most righteous man on earth at the time, then I don't think you can claim you know whether He would harden the heart of the the elect.
I think you are confusing apples and oranges.
Trials are not the same as hardening.
And yes I can say He will not harden one of the elect.
Phil 1:6: And I am sure of this, that he who began a good work in you will bring it to completion at the day of Jesus Christ.
Romans 8:31 What, then, shall we say in response to this? If God is for us, who can be against us? 32He who did not spare his own Son, but gave him up for us all—how will he not also, along with him, graciously give us all things? 33Who will bring any charge against those whom God has chosen? It is God who justifies. 34Who is he that condemns? Christ Jesus, who died—more than that, who was raised to life—is at the right hand of God and is also interceding for us. 35Who shall separate us from the love of Christ? Shall trouble or hardship or persecution or famine or nakedness or danger or sword? 36As it is written:
“For your sake we face death all day long;
we are considered as sheep to be slaughtered.”l
37No, in all these things we are more than conquerors through him who loved us. 38For I am convinced that neither death nor life, neither angels nor demons,m neither the present nor the future, nor any powers, 39neither height nor depth, nor anything else in all creation, will be able to separate us from the love of God that is in Christ Jesus our Lord.