It is usual to address the President as: “Dear Mr. President,” and close with “Respectfully yours.” For other officials, use their title and last name, and close with “Sincerely yours.”

US President

President (full name)
The White House
1600 Pennsylvania Avenue NW
Washington, DC 20500
Dear Mr. President

US Senator

The Honorable (full name)
Washington DC address or Colorado address
Dear Senator (last name)

US Representative

The Honorable (full name)
US Representative
Washington DC address or Colorado address
Dear Congressman/Congresswoman (last name)

State Senator

Senator (full name)
Colorado State Capitol
200 E. Colfax
Denver, CO 80203 or home address

State Representative

Representative (full name)
Colorado State Capitol
200 E. Colfax
Denver, CO 80203 or home address