Since 1790, when two U.S. patent applicants have claimed the same invention, the patent has been awarded to the first inventor. Today, the United States stands alone in the industrialized world, and many argue that the United States should, in the interest of world patent harmony, change its system so as to award a contested patent to the first applicant. Of the arguments advanced to justify the change, the only ones that withstand scrutiny are that "all the other countries are doing it" and the hope that some concessions in other aspects of intellectual property or trade might be obtained in exchange. There are compelling reasons to resist the change, principally that (unless other fundamental aspects of U.S. patent law are changed as well) U.S. inventors will be disadvantaged.
Even if the arguments favoring the change are found to outweigh the arguments favoring the status quo, the power to grant U.S. patents derives from Article I, Section 8, Clause 8 (the Intellectual Property Clause) of the Constitution, which authorizes granting exclusive rights to authors and inventors. Other countries are not so constrained. An historical analysis of the Intellectual Property Clause and review of the types of evidence used by the Supreme Court in constitutional analysis lead to the conclusion that the Intellectual Property Clause does not permit granting patents to the first applicant in preference to the first inventor.
Alternate sources of Congressional power have been suggested (principally the Commerce Clause and the Treaty Power), but the Supreme Court has never found either sufficient to overcome a specific constitutional limitation of power. The only power which seems sufficient to accomplish the objective of harmonization within constitutional limits is eminent domain.