Vermont is one of only six states—along with Connecticut, Massachusetts, Hawaii, Rhode Island and Delaware—where every House Representative and Senator is Democratic. In Vermont, Patrick Leahy and Bernie Sanders are the Senators. (Sanders is technically an Independent but is allied with the Democrats). Peter Welch, a Democrat, is the sole representative.
At the opposite end of the spectrum, eight states (Oklahoma, Arkansas, Kansas, Utah, Idaho, Alaska, South Dakota and Wyoming) are entirely represented by Republicans.
Oddly, the opposite was true for both the Senate and the House for most of Vermont's history.
Starting in 1855, every single Senator from the state of Vermont was a Republican . Patrick Leahy was the first Democrat elect in 1974. Jim Jeffords was elected as a Republican in 1989 but switched to a Democrat in 2001 after the party moved too far away from "Vermont values." Jeffords was followed in 2007 by Bernie Sanders.
In the House of Representatives, 32 straight Republicans were elected between 1856 and 1959 (except for a "Greenback" party candidate from 1879 to 1891). A Democrat then served a single term form 1959 to 1961 and was then replaced by a Republican for the next 30 years until Bernie Sanders was elected in 1991. He was followed by Democrat Peter Welch in 2007.