Answer: Yes it's theoretically possible
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Step-by-step explanation:
Article IV, section 3 of the US Constitution states:
New States may be admitted by the Congress into this Union; but no new States shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.
As the latter part mentions, two or more states could theoretically join together to form a larger new state (the previously mentioned states would then be dissolved). This joining is only possible if both conditions are met:
- a) each state legislature, of those states who are merging, agrees to the terms
- b) congress itself agrees to the terms