First, under our Constitution, while the president negotiates international agreements, Congress plays the significant role of ratifying them. In the case of a treaty, the Senate must ratify it by a two-thirds vote. A so-called congressional-executive agreement requires a majority vote in both the House and the Senate (which, because of procedural rules, effectively means a three-fifths vote in the Senate). Anything not approved by Congress is a mere executive agreement.

Second, the offices of our Constitution have different characteristics. For example, the president may serve only two 4-year terms, whereas senators may serve an unlimited number of 6-year terms. As applied today, for instance, President Obama will leave office in January 2017, while most of us will remain in office well beyond then—perhaps decades.