NEW YORK — Most Americans want Congress to extend tax credits that, if left to expire at the end of the year, could raise health insurance costs for millions of Americans, according to a new poll released Friday from the health care research nonprofit KFF. A Senate standoff, in part over the enhanced premium tax credits set to end if Congress doesn't act, resulted in a government shutdown that's lasted into a third day with no end in sight. The vast majority of Democrats supported the extended tax credits, the poll found, but so did a slimmer majority of Republicans. According to the KFF poll, about 3 in 4 Americans — 78% — said they wanted Congress to extend expiring tax credits for people who buy health insurance through the ACA marketplace. About 6 in 10 people who self-purchased insurance said they heard "a little" or "nothing" about the tax credits' expiration.