Article 2, Section 1, Clause 5
Joseph Story, Commentaries on the Constitution 3:§§ 1472--731833
§ 1472. Considering the nature of the duties, the extent of the information, and the solid wisdom and experience required in the executive department, no one can reasonably doubt the propriety of some qualification of age. That, which has been selected, is the middle age of life, by which period the character and talents of individuals are generally known, and fully developed; and opportunities have usually been afforded for public service, and for experience in the public councils. The faculties of the mind, if they have not then attained to their highest maturity, are in full vigour, and hastening towards their ripest state. The judgment, acting upon large materials, has, by that time, attained a solid cast; and the principles, which form the character, and the integrity, which gives lustre to the virtues of life, must then, if ever, have acquired public confidence and approbation.
§ 1473. It is indispensable, too, that the president should be a natural born citizen of the United States; or a citizen at the adoption of the constitution, and for fourteen years before his election. This permission of a naturalized citizen to become president is an exception from the great fundamental policy of all governments, to exclude foreign influence from their executive councils and duties. It was doubtless introduced (for it has now become by lapse of time merely nominal, and will soon become wholly extinct) out of respect to those distinguished revolutionary patriots, who were born in a foreign land, and yet had entitled themselves to high honours in their adopted country. A positive exclusion of them from the office would have been unjust to their merits, and painful to their sensibilities. But the general propriety of the exclusion of foreigners, in common cases, will scarcely be doubted by any sound statesman. It cuts off all chances for ambitious foreigners, who might otherwise be intriguing for the office; and interposes a barrier against those corrupt interferences of foreign governments in executive elections, which have inflicted the most serious evils upon the elective monarchies of Europe. Germany, Poland, and even the pontificate of Rome, are sad, but instructive examples of the enduring mischiefs arising from this source. A residence of fourteen years in the United States is also made an indispensable requisite for every candidate; so, that the people may have a full opportunity to know his character and merits, and that he may have mingled in the duties, and felt the interests, and understood the principles, and nourished the attachments, belonging to every citizen in a republican government. By "residence," in the constitution, is to be understood, not an absolute inhabitancy within the United States during the whole period; but such an inhabitancy, as includes a permanent domicil in the United States. No one has supposed, that a temporary absence abroad on public business, and especially on an embassy to a foreign nation, would interrupt the residence of a citizen, so as to disqualify him for office. If the word were to be construed with such strictness, then a mere journey through any foreign adjacent territory for health, or for pleasure, or a commorancy there for a single day, would amount to a disqualification. Under such a construction a military or civil officer, who should have been in Canada during the late war on public business, would have lost his eligibility. The true sense of residence in the constitution is fixed domicil, or being out of the United States, and settled abroad for the purpose of general inhabitancy, animo manendi, and not for a mere temporary and fugitive purpose, in transitu.
The Founders' Constitution
Volume 3, Article 2, Section 1, Clause 5, Document 2
The University of Chicago Press
Story, Joseph. Commentaries on the Constitution of the United States. 3 vols. Boston, 1833.