How is the president's power to pardon in case of impachment limited?

[JDPriestly]

Someone asked a question of this nature the other day here on DU. I can't give a definitive answer, but I would like to offer the following information for discussion:

U.S. Constitution, Article 2, Section 4

Section 4. The President, Vice President and all civil officers of the United States, shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanors.

In Federalist Paper No. 69, Hamilton wrote:

. . . The power of the President, in respect to pardons, would extend to all cases, EXCEPT THOSE OF IMPEACHMENT. The governor of New York may pardon in all cases, even in those of impeachment, except for treason and murder. Is not the power of the governor, in this article, on a calculation of political consequences, greater than that of the President? All conspiracies and plots against the government, which have not been matured into actual treason, may be screened from punishment of every kind, by the interposition of the prerogative of pardoning. If a governor of New York, therefore, should be at the head of any such conspiracy, until the design had been ripened into actual hostility he could insure his accomplices and adherents an entire impunity. A President of the Union, on the other hand, though he may even pardon treason, when prosecuted in the ordinary course of law, could shelter no offender, in any degree, from the effects of impeachment and conviction. Would not the prospect of a total indemnity for all the preliminary steps be a greater temptation to undertake and persevere in an enterprise against the public liberty, than the mere prospect of an exemption from death and confiscation, if the final execution of the design, upon an actual appeal to arms, should miscarry? Would this last expectation have any influence at all, when the probability was computed, that the person who was to afford that exemption might himself be involved in the consequences of the measure, and might be incapacitated by his agency in it from affording the desired impunity? The better to judge of this matter, it will be necessary to recollect, that, by the proposed Constitution, the offense of treason is limited "to levying war upon the United States, and adhering to their enemies, giving them aid and comfort"; and that by the laws of New York it is confined within similar bounds. Fourthly. The President can only adjourn the national legislature in the single case of disagreement about the time of adjournment. The British monarch may prorogue or even dissolve the Parliament. The governor of New York may also prorogue the legislature of this State for a limited time; a power which, in certain situations, may be employed to very important purposes.

http://www.foundingfathers.info/federalistpapers/fedindex.htm

In fact, treason is not the only ground for impeachment as Hamilton states in Federalist Papers No. 65:

A well-constituted court for the trial of impeachments is an object not more to be desired than difficult to be obtained in a government wholly elective. The subjects of its jurisdiction are those offenses which proceed from the misconduct of public men, or, in other words, from the abuse or violation of some public trust. They are of a nature which may with peculiar propriety be denominated POLITICAL, as they relate chiefly to injuries done immediately to the society itself. The prosecution of them, for this reason, will seldom fail to agitate the passions of the whole community, and to divide it into parties more or less friendly or inimical to the accused. In many cases it will connect itself with the pre-existing factions, and will enlist all their animosities, partialities, influence, and interest on one side or on the other; and in such cases there will always be the greatest danger that the decision will be regulated more by the comparative strength of parties, than by the real demonstrations of innocence or guilt.
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Do you have any comments? any additional information on the limits on the president's pardon powers in case of impeachment?