The party Lincoln founded on grand ideals of inclusion and reform has evolved into a party of ideological and racial purity, the very thing that it was founded to oppose. The Know-Nothings, Whigs, and Dixiecrats have taken over, leaving only one umbrella party in control of this country's governance, and in a non-Parliamentary republic, single-party rule is bad.
It would be nice to see a genuinely reform-minded, visionary minority (Mel Martinez? Bobby Jindal? Colin Powell? perhaps Christy Whitman?) rise to national prominence and take that party back where it came from: a grand umbrella, embracing conservative (as opposed to reactionary) voices from all over the political and economic spectrum, from the socially-moderate, fiscally conservative Ron Steeles and Colin Powells to the socially-conservative, working-class Reagan Democrats (who are mainly immigrants, overwhelmingly Catholic or Evangelical.) If they could manage that, we might have a meaningful contest between grand parties and a useful argument about what services government should be providing its citizens: foreign policy, "common needs" services like roads and clean water and health care, and policing. If they don't, we'll likely be stuck with what we've got now: a party in total control of an agenda they haven't well defined on account of not anticipating such overwhelming support from the electorate, and another in near-disintegration on account of allowing its loudest (read: least coherent, most fearful) voices to guide its policy decisions instead of a rational, frankly elitist discussion among its wisest members.
Single-party rule, both short-term and long-term, is never good for a two-party system. In a Parliamentary democracy, it's all right to plead "no contest" for an election or two. In a two-party republic, it never is.