In addition, Democratic Vermont Gov. Peter Shumlin beat Republican challenger Randy Brock to win another two-year term in Montpelier.
Obama tallied more than 67 percent of the popular vote to Romney's 43 percent, with almost all the votes counted. Vermont has three electoral votes.
Obama won every county in the state in 2008 -- all but one of them with at least 60 percent of the vote. He also won 247 out of the state's 251 cities and towns, the Almanac of American Politics says.
Sanders, who caucuses with Democrats, defeated Republican John MacGovern, 71 percent to 25 percent, with almost all votes counted.
Sanders, 71, is Vermont's junior senator, serving with Patrick Leahy, the state's first and only elected Democratic senator. Sanders previously represented Vermont's at-large district in the House and served as mayor of Burlington, Vermont's largest city.
MacGovern unsuccessfully ran for the Vermont Senate in 2004 and 2006.
Welch, the state's at-large House representative, beat Republican Mark Donka, 72 percent to 23 percent, with almost all votes counted.
Donka is a police officer and former member of the Hartford, Vt., Board of Selectmen,
Shumlin defeated Brock, 58 percent to 38 percent, with almost all votes counted.
Shumlin, 56, is Vermont's 81st governor, first elected in 2010.
Brock served as state Auditor of Accounts from 2005 to 2007.