WASHINGTON  The midterm election campaign will end Tuesday, but one of its most marked developments  the emergence of outside groups, often backed by anonymous donations, that can direct waves of advertising into political battles  is just getting started.

Buoyed by the impact their blistering, anti-Democratic campaigns have had this year, two of the largest new conservative groups helping Republicans are planning to keep pushing their agenda in the lame-duck session of Congress that will begin in two weeks and are already laying the groundwork for a more aggressive campaign in the 2012 presidential race.

That development is causing Democrats to reassess their early financial plans for President Obama’s re-election campaign while forcing them to balance the administration’s demands for more transparency in campaign finance against the pressure for liberal groups to do more to counteract the strength of their conservative counterparts.

Officials with the two conservative groups, American Crossroads and Crossroads GPS  which are on track to spend well over $50 million combined this year, a sizable part of it from undisclosed donors  said they would continue advertising against Democrats as Congress returns, when decisions loom on the extension of the Bush-era tax cuts and immigration.