Dion campaigned on environmental sustainability during the leadership race, and created the "Green Shift" plan following his election as leader. The Green Shift proposed creating a carbon tax that would be coupled with reductions to income tax rates. The proposal was to tax greenhouse gas emissions, starting at $10 per tonne of CO2 and reaching $40 per tonne within four years. The plan was a key policy for the party in the 2008 federal election, but it was not well received and was continuously attacked by both the Conservatives and NDP. On election night the Liberal Party won 26.26 percent of the popular vote and 77 of the 308 seats in the House of Commons. At that time their popular support was the lowest in the party's history, and weeks later Dion announced he would step down as Liberal leader once his successor was chosen.