They effectively had a 60-seat senate majority for only 3 months at the end of 2009. They had three months prior to that but had two seriously Ill Senators,
Kennedy and Byrd, who were unavailable for votes. Even when they had 60, Byrd was barely available.
The real failure is that Obama ran an inspirational campaign in 2008, then turned to milquetoast centrism the second he took office. That led to suppressed voter enthusiasm and the Democrats got clobbered in the 2010 midterms.