Due diligence requires asking and answering how prospective judges support the Constitution.
October 1, 2020 drafted
October 16, 2020 published
A prospective judge’s existing knowledge base  will figure into the judge’s future opinions.
On future cases, facts are not yet known; but on most future cases, the law  is already known.
A candidate who withholds any current opinions on existing law while a president is nominating or while senators are advising and consenting  is not performing the job of a candidate. Such nonperformance strongly suggests that if appointed, the candidate would also not perform the job of a judge on some cases or on many cases.
A president who nominates a candidate who withholds any current opinions on existing laws, or a senator who advises in favor of and consents to such a candidate, is not representing we the people.
Life, Then Liberty, Then Property
Judges’ opinions on past cases are not law on future cases, so a candidate’s current opinions on those past cases are not the opinions that are needed.
Since past judges’ opinions shouldn’t matter, presidents and senators should make past judges’ opinions not matter. Presidents and senators should not question candidates about past judges’ opinions.
Constitutionally, a judge on the Supreme Court, like all state and national civil officers other than the president, must take an oath or affirmation  to support the Constitution . Also, constitutionally, the existing law that’s supreme  is the Constitution.
This means that when considering nominating, and when advising and considering consenting, the questions about existing law that are supreme are questions about the Constitution.
Like all law , the Constitution consists of rules and sanctions.
In the Constitution, the sanctions aren’t specific penalties associated with specific rules but rather are various offsetting powers. Each offsetting power comes into play to enforce a given rule only if the rule is first transgressed. So the necessary starting point in supporting the Constitution is to have constitutionally-correct opinions on the Constitution’s rules.
Most of the Constitution’s rules are supporting rules that help secure more-fundamental rules. The most-fundamental rules  aren’t at all equal; rather, they form a hierarchical sequence: life must be made secure before liberty becomes primary, liberty must be made secure before property becomes primary, and property must be made secure then—all types of property, and each aspect of each type.
The primacy of these bedrock rights, and also this hierarchy, are violated by major unconstitutional opinions of past Supreme Courts. Majority opinions in favor of abortion destroy life, supposedly to secure liberty. Majority opinions in favor of Progressive social changes destroy religious liberty and destroy liberty to use one’s property as one chooses, supposedly to secure other, extraconstitutional rights.
To represent we the people when nominating and when advising and consenting on judges on the Supreme Court, presidents and senators must ask, obtain, and weigh prospective judges’ opinions on the Constitution’s rules on life, liberty, and property:
No Person Shall Be Deprived of Life …
No Person Shall Be Deprived of Liberty …
No Person Shall Be Deprived of Property …
If most current senators don’t support constitutionalists for the Supreme Court, we the people can live with a vacancy or vacancies until we elect new senators who will.
We need at least some presidents and senators who don’t game the outcome but just do the right thing and let the chips fall as they may. If at least some presidents and senators currently will do due diligence before filling a seat , then we still have some representation and a conceivable path to elect more senators who will.
But if no presidents and no senators request information about prospective nominees’ support for the Constitution, and provide informed nomination, informed advice, and informed consent, then we the people are being subjected to rule with no representation, and the current governance by the people in all branches of the national government is illegitimate.