The United States has five inhabited territories: Guam, Mariana Islands, Puerto Rico, US Virgin Islands, and the American Samoa.
Puerto Rico has been a U.S. territory since 1898 (acquired as a result of the Spanish-American War). Since 1917, Puerto Ricans have had U.S. citizenship. But, they do not have a voting member in Congress and are not able to vote in the Presidential election. This past election, the citizens of Puerto Rico voted to decide their political status in relation to the United States. They voted for statehood. But, no state has achieved statehood in the same way--and there is no Constitutional guidance for a territory to become a state.
The President, and Congress, should develop a system for U.S. territories to achieve statehood and full rights as U.S. citizens.