To what extent are the Republican and Democratic parties ideologically distinct?

Historical opponents, the Republican and Democratic parties were established upon contrasting and conflicting ideological traditions of classical liberalism and federalism. As such, the ideologies expressed by the parties today are starkly different, expressing different priorities and public policy prescriptions based upon their differening foundations and the constituencies they now serve. On one hand, the Republican Party exhibits American conservatism, emphasising small-government, fiscal responsibility, and individual liberty within a constitutional republic, as well as a distinctly Judeo-Christian ethic. Conversely, the Democrats Party exhibits progressivism, seeking to advance a welfarist, expanded vision of the American state, with particular concern for environmental matters, and social and political justice - defined, largely, by equality of outcome and opportunity. A particular area of constrast would be gun-policy, which, motivated by recent mass shootings and a public interpretation of expanded gun violence, has come to the fore of American political discourse. The Republican Party generally favours the minimisation of regulation upon firearms, believing the 2nd Amendment, as confirmed in the case of D.C. v. Heller, to principally establish an individual right founded upon a need to resist the threat of tyrannical government, and ensure individual safety from harm. The Democratic Party, on the other hand, generally favoursthe greater regulation of guns, believing the 2nd Amendment to be either out-dated (a result of their constructivist judicial philosophy, whereby the articles of the Constitution are expected to develop and alter with changing social and political circumstances) or not indicative of an individual right. This has motivated a series of positions, including, among the left of the party, a desire for the mandatory repurchase of all firearms in the US, and, towards the centre, the greater limitation of access to weapons - mandating expanded background checks and safety training. The matter of firearms exhibits neatly the divide between the Republicans and Democrats - tradition versus modernity, and principle versus a sense of practicality.