Sen. Daniel Inouye will almost certainly be elected President pro tempore of the Senate

According to 8 U.S.C. § 1408, it is possible to be a U.S. national without being a U.S. citizen. A person whose only connection to the U.S. is through birth in an outlying possession (which as of 2005 is limited to American Samoa, Swains Island, and the unincorporated US Minor Outlying Islands), or through descent from a person so born, acquires U.S. nationality but not U.S. citizenship. This was formerly the case in only four other current or former U.S. overseas possessions
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Not all U.S. nationals are U.S. citizens; all U.S. citizens are U.S. nationals. The U.S. passport issued to non-citizen nationals contains the endorsement code 9 which states: "THE BEARER IS A UNITED STATES NATIONAL AND NOT A UNITED STATES CITIZEN." on the annotations page. Noncitizen U.S. nationals may reside and work in the United States without restrictions, and may apply for citizenship under the same rules as resident aliens.

Like aliens, U.S. nationals who are not citizens are not prevented from voting in state and federal elections by the federal government, but are not allowed by any U.S. state to vote in federal elections.

U.S. nationals who become citizens are not considered natural-born.

§4. Citizenship. That all persons who were citizens of the Republic of Hawaii on August twelfth, eighteen hundred and ninety-eight, are hereby declared to be citizens of the United States and citizens of the Territory of Hawaii.

And all citizens of the United States resident in the Hawaiian Islands who were resident there on or since August twelfth, eighteen hundred and ninety-eight and all the citizens of the United States who shall hereafter reside in the Territory of Hawaii for one year shall be citizens of the Territory of Hawaii.