In the [Constitutional] convention George Mason argued that the President might use his pardoning power to “pardon crimes which were advised by himself” or, before indictment or conviction, “to stop inquiry and prevent detection.”
James Madison noted:
[I]f the President be connected, in any suspicious manner, with any person, and there be grounds tp believe he will shelter him, the House of Representatives can impeach him; they can remove him if found guilty
J. Elliot noted this in The Debates in the Several State Conventions on the Adoption of the Federal Constitution 74. Elliot further noted:
the President could be suspended when suspected, and his powers would devolve on the Vice President, who could likewise be suspended until impeached and convicted, if he were also suspected.
James Madison’s wisdom certainly applies today.