When he received his pardon, Van Schaick had served three-and-a-half years of his 10-year sentence in Sing Sing, but had been paroled earlier in 1912. His wife and other supporters had been campaigning for clemency since his sentencing. President Roosevelt had declined to pardon Van Schaick, but President Taft decided otherwise. Naturally, the decision upset many others, especially relatives of those who died on the General Slocum and their sympathizers.
Yet the president was within his rights. Article II, Section 2 of the Constitution gives him broad pardoning powers: "The President ... shall have power to grant reprieves and pardons for offenses against the United States, except in cases of impeachment."
Jurist, which is maintained by the University of Pittsburgh School of Law, notes that there have been attempts to curtain that authority: "Shortly after President Gerald Ford’s controversial pardon of Richard Nixon in 1974, then-Senator Walter Mondale of Minnesota proposed an amendment to the Constitution that would have added the following sentence to the pardon clause: 'No pardon granted an individual by the President under section 2 of Article II shall be effective if Congress by resolution, two-thirds of the members of each House concurring therein, disapproves the granting of the pardon within 180 days of its issuance.'
"In 1993, a member of the House of Representatives introduced a Resolution proposing the following language: 'The President shall only have the power to grant a reprieve or a pardon for an offense against the United States to an individual who has been convicted of such an offense.'... In 2000, the proposed Crime Victims Rights Amendment provided that a victim of crime or violence had the right 'to reasonable notice of and an opportunity to submit a statement concerning any proposed pardon or commutation of a sentence.' "
None of these efforts went anywhere. President Obama has essentially the same pardoning power that President Washington did (who used it sparingly, however, pardoning only 16 people in his two terms).