Can the president stop an impeachment like this if both and House and Senate are on board?
No. But if you cannot get 2/3 in the Senate the impeachment fails. The Dems will vote against conviction in a Senate trial and it will fail. But it will reveal them all to be on the side of corruption and political persecution of enemies.
“Can the president stop an impeachment like this if both and House and Senate are on board?”
No. And I doubt he’d spend the political capital. The IRS chief, if impeached, will be given a cushy job at a left wing NGO and a thank you for taking one for the team.