MONTPELIER — A new poll shows Democrat Peter Welch has established a small lead in the race to succeed Rep. Bernard Sanders, one of a few dozen contests that could help to determine control of Congress next year. The poll found that if the election were held now, Welch would get the vote of 45 percent and Martha Rainville, the Republican nominee, would get 39 percent. The poll said other candidates would get 2 percent of the vote and 14 percent of respondents were undecided. WCAX-TV commissioned the poll from Research 2000 of Rockville, Md. A total of 400 likely...