( CNN ) -- As this election season unfolds , we are watching an age-old dream in politics go horribly smash . It is n't good for politics , and it sure is n't good for the country . President Franklin Roosevelt helped to fire up the dream during his second term in office . Coming off a massive landslide in 1936 , he believed that it would be far better for governing if the Democrats became the liberal party and Republicans the conservative one . In the 1938 congressional elections , he barnstormed across the South trying to purge the Democratic Party of several incumbent conservatives . His efforts backfired -- the incumbents won and were sore at FDR -- but the dream became a staple of politics . In 1950 , for example , in one of the landmark studies in political science -- one still read today by undergraduate majors -- some of the best minds of the day argued strongly that the nation would benefit from more ideologically `` coherent '' parties : that things would be better if Democrats stood firmly for a liberal ideology and Republicans for a conservative one . That way , people would have clear choices , they would know what they were voting for , and they could count on their party delivering if it were in power . `` Shoo out those racially suspect Sunbelt conservatives from Democratic ranks and those lily-livered Northeastern liberals from the GOP . And maybe some of those moderates , too . '' So the thinking went . Well , in recent years , we have seen the dream come true . And guess what ? It is producing a mess . As each of the parties has moved toward ideological purity , our politics have become ever more polarized , our governing ever more paralyzed . Extremists increasingly run the show . This campaign season is pointing toward a rough road ahead after the November elections . Yes , it is true that in selecting a presidential candidate , both parties have chosen men who on the surface seem moderate centrists . But each of the candidates has decided that in order to win , he must first stir up his ideological base . Would Mitt Romney have endorsed the Paul Ryan budget , a hard line against immigration and a condemnation of Planned Parenthood if he were not trying to prove that he 's a `` severe conservative '' ? Meanwhile , Barack Obama has moved left , pushing taxes on the rich , piling up trillion-dollar deficits and bashing the same Republicans he would have to work with in a second term . One can see these trends in harsher relief amid campaigns for the Senate and House . Olympia Snowe , a moderate and much-beloved GOP senator from Maine facing her first primary challenge , is retiring because of a lack of bipartisanship and mechanisms to find `` common ground . '' Sens . Richard Lugar and Orrin Hatch -- both stalwarts of the GOP who have committed apostasy by trying to work across party lines -- face primaries this season that imperil their survival : A poll Thursday morning found Lugar down 5 points to a tea party-backed challenger in Indiana , and Hatch failed to secure a 60 % supermajority at his party 's convention in Utah , sending his race to a primary . Only two years ago in Utah , another stalwart Republican who had worked with Democrats , Bob Bennett , was deposed by an ideologically purer primary challenger . In the House , meanwhile , the once-robust cadre of `` Blue Dog Democrats '' -- moderate to conservative members of the liberal party -- has been winnowed out , with two more members ( Reps. Jason Altmire and Tim Holden of Pennsylvania ) defeated in primaries this past Tuesday by opponents from their left flanks . As of 2010 , there were as many as 54 Blue Dogs , but the midterms knocked their caucus down to 26 . With retirements and primaries , that number will probably be well below 20 by next January -- an effect that further turns Democrats into the party of the left . Some activists -- conservative Grover Norquist among them -- argue that over time , this purification will be good for the U.S . But so far , the task of governing has gotten much tougher , and what little trust is left among the parties is evaporating . As the parties become more ideological , it 's easier to demonize the other side and harder to rationalize working with it -- both to your colleagues and your constituents . Woe to be you in your next primary if you have consorted with the enemy . Under heavy pressures for party conformity , legislation by nature becomes a more partisan undertaking . Hard to believe it now , but big programs like Medicare and Medicaid in the 1960s , or tax and Social Security reform in the 1980s , passed with broad bipartisan support . Our latest legislative achievements , on the other hand ( think health care , the stimulus or Wall Street reform ) , have been almost entirely driven by one party . More often than not , gridlock and obstruction soon follow . As scholar Bill Galston has wisely noted , it becomes `` a zero-sum mentality : if they win , we lose . '' As Galston and others have theorized , all this sniping saps the public 's trust in the government , but it does something equally insidious , too : It saps trust between the parties , completing the vicious cycle and making compromise even tougher . So it 's crucial to bolster the men and women of courage in politics : the ones who can act as ambassadors between these increasingly dug-in parties and who can kindle that small flame of trust that has almost gone out . Sens . Lamar Alexander ( R-Tennessee ) and Mark Warner ( D-Virginia ) and a handful of others , for example , have launched laudable work on this count in the Senate , pulling together small , quiet dinners with legislators from both sides of the aisle who are strong in principles but equally strong in their commitment to moving the ball forward for the country . Getting by on the little victories can help restore health to the process , too . The Congress coming together on patent reform at the end of 2011 , the JOBS Act in early April and ( potentially ) on extending low interest rates on student loans in coming days may seem like small potatoes , but these compromises can be confidence builders . Like water over a stone , they can slowly but steadily wear away some of the mistrust and acrimony . Franklin Roosevelt was right on many big things , but on this one , he was dead wrong . The opinions expressed in this commentary are solely those of the authors .
From FDR in the 1930s on , some have argued that parties should be polarized . We 're seeing consequences of Dems as liberal party , GOP as conservative one , authors say . Comment: Gergen , Zuckerman : Obama , Romney have been firing up ideological base of their parties .