Congrats on your internship! I answered a somewhat similar question to this before. You can read that here, so I won’t rehash everything there.
Not sure what your budget is, but I’d say get at least one suit and one blazer, a few dress shirts, a few ties, some grey trousers and maybe a v-neck sweater or sweater vest (cashmere or wool, depending on your budget) for when you want to dress down a bit or layer up, two good pairs of shoes with matching belts.
I’m not sure if you’re working in a district office or on the Hill, but if it’s in a district office you might be able to just get away with one well-fitting navy blazer instead of the suit. Although, I’d argue that having a suit on hand is never a bad thing and an essential for every guy’s wardrobe.
If you’re on the ramen-noodle budget and looking for specific brands to buy new at retail, then I’d recommend the following:
- Suit: Lands’ End tailored fit suit separates (sign up for their email list, wait for 30% off entire purchase coupon code, happens every few weeks)
- Blazer: Lands’ End Canvas or LLBean Signature have a lot of options. If you want something more classic though, I suggest hitting up a thrift store or eBay. Both have an infinite supply of navy blazers. Just find one that’ll fit in the shoulders and length and have it tailored to your arms and chest. That’s what I did.
- Shirts: I’d recommend Brooks Brothers Extra Slim Fit shirts. A bit more pricey for off-the-rack, but the fit is good and they go to exact neck/sleeve sizes. I haven’t really found others that match the fit/price.
- Shoes: Allen Edmonds right now is down to $200 at Nordstrom, but you could probably find a few used options for much less on eBay.
- Ties: The Tie Bar at the lowest end has a good selection for the price. Quality’s on par with any other “made in China” neckwear. If there’s a Nordstrom Rack near you, hit them up. Lots of their neckwear is pretty meh, but if you can find their Nordstrom 1901 line, they usually sell for $10 and are made in the USA. For silk knits, I’d suggest Lands’ End.
The good news is that you’ve got a few months to plan ahead and start scouring for deals on eBay and StyleForum’s Buy & Sell classifieds. If you don’t know your measurements yet, get that done (plenty of resources online to help you out). You could potentially score some better quality stuff at lower prices. Time’s somewhat on your side.
As far as general advice, I would recommend just working hard, don’t blog/Facebook/Twitter about work and give and ask for as many business cards as you can (and always have yours with you — I store a few in every jacket I own so I always have one).
Oh, and while the job is inherently political and perhaps partisan, just keep an open mind to those on the other side of things. I work for Republicans, but I maintain friendships with people on both sides of the divide. I try to find open-minded people, because they’re much more interesting to be around and you’ll learn more.