The impeachment clause was designed to protect our country against a President who was using his official powers against the nation, against the American people, against our society. Grand juries are not designed to search for truth. They do not and are not intended to ensure credibility, reliability, or simple fairness. They only exist to accuse. The law defines perjury very clearly.
Perjury requires proof that an individual knowingly made a false statement while under oath.
Answers to questions that are literally true are not perjury. Answers to fundamentally ambiguous questions also can never be perjury. The President did not commit perjury. Most of the illegal leaks suggesting his testimony was perjurious falsely describe his testimony. First of all, the President never testified in the Jones deposition that he was not alone with Ms. Lewinsky.