Here are some tips:

• Use "Inquiring about Internship Availability" for your email subject line.
• Address the internship coordinator by name if possible.
• Start by introducing yourself – give your school and major.
• Tell them that you will be in DC with the Washington Program in <Quarter Year> and are interested in interning with them.
• Write a sentence or two expressing why you want to work for them specifically.
• Tell them the specific dates that you will be in DC and ask whether they offer an internship during this time, and if so, how to apply.
• Thank them for their time.