The President acted outside of his constitutional authority when he controlled the nomination of Judge Kavanaugh to the U S Supreme Court from the White House.
Senate Republicans abdicated and violated their constitutional duties and responsibilities when they collaborated with the White House to obstruct Senate Democrats from obtaining Kavanaugh's complete records of his tenure in the White House Counsel's office during the Bush '43 administration, and limiting the FBI's investigation into the numerous allegations of sexual assault against Kavanaugh.
There's no provision in the US Constitution which authorizes the President to nominate judges from a list prepared by a political interest group (right or left wing) such as The Federalist Society. The US Constitution confers the duty and authority of "advice and consent" exclusively upon the members of the US Senate. In choosing a nominee for the federal bench, The President has no authority to seek "advice" from any other persons, officials, entities, or groups. The President failed to seek the advice of any Senator prior to nominating Kavanaugh. Senator McConnell acknowledged as much when he stated that he "wished the President had nominated someone other than Kavanaugh because of the "difficulty" of getting him through the nomination process.
Once the President nominates a person for the federal bench- which should have been WITH the advice of the Senate-neither the President nor White House Counsel McGahn (whose position, title, and duties are NOT EVEN IN the US Constitution) has the authority to orchestrate, control, limit, or direct the Senate's investigation into the nominee's background, qualifications, and character. Doing so usurped the Senate's "advice" role .
There's no provision in the US Constitution that gives more power over to judicial appointments to Senate members of a particular political party. In fact,that the US Constitution doesn't even provide for the formation, powers, or authority of political parties.
Senate Republikkklans abdicated their responsibility to conduct a full and fair investigation of Kavanaugh, and violated the US Constitution in collaborating with the White House in withholding from the full Senate, information regarding Kavanaugh's tenure in the Bush '43 White House Counsel's office.
Senate Democrats should have gone to federal court if necessary to obtain an injunction barring the President from : (1) choosing a nominee from a list compiled by the Federalist Society; and (2) barring White House Counsel McGahn from stonewalling the Senate's deliberations and full investigation of Kavanaugh. In not doing so, the Democrats made a strategic blunder from which the US Supreme Court and the nation may not recover for generations.