Here are some tips for inquiring about an internship opportunity with a researcher or research team: 

• For this type of email, you will essentially be writing your cover letter in the body of your email. Researchers are very busy people so you want to express right away why you want to work with them.
• Explain who you are and that you will be in Washington D.C. with the program.
• Be sure to reference work of theirs that you find interesting. A little bit of flattery goes a long way!
• Convince them of the skills that you are able to offer them, especially previous research experience.
• Be sure to really emphasize why you want to work with this person in particular.
• Keep the email relatively concise.