The liberal Democrats have seen their support rate increase in recent weeks after many in the public blamed Lee and the GNP for a graft probe of former President Roh Moo-hyun that may have led to his suicide.
South Korea's financial markets, used to the political polarisation and delays in parliament, have not set their hopes too high on any major reforms being implemented quickly.
Another contentious law pushed by the GNP, is a bill allowing for the cross ownership of newspapers and broadcasters.
The Democrats called it an "evil law" that would end the independence of TV broadcasters, who currently receive state funding. The GNP says it will help modernise a broadcasting industry that has become too dependent on government handouts.
(Additional reporting by Christine Kim and Seo Eun-kyung; Editing by David Fox)