The historical reality is that the political philosophies of the parties has literally done a compete 180 since the Civil War. In the 1860s, the democrats were, for the most past, sympathetic to some degree with the Confederacy. Lincoln's reelection campaign in 1864 was seriously challenged by former commander of the Army of the Potomac, Gen. George McClellan being the democratic nominee. Their platform revolved around an end to conscription and they vociferously disagreed with Lincoln's decision to issue the Emancipation Proclamation in 1863. They were in favor of pursuing an end to the war by whatever fashion might prove practical. Not exactly a "liberal" stance (even the end-the-war campaign was based much more on personal belief and economic reasons as opposed to being "anti-war" in any aspect) any way you look at it.
The pivotal moment that engendered the big reversal was the civil rights movement that began to be adopted by the democratic party in the late 1940s. Prior to that, the democrats were perceived to be by far the more reactionary party, especially as it pertained to racial relations....so much so that the bloc of southern states that primarily comprised the core of the former Confederate States of America was openly referred to as the "Solid South" back in the day due to their reliable predisposition to vote democratic. However, when Truman invoked Executive Order 9981 (racial equality in the US military) in 1948 followed by the landmark Brown v Board of Education SCOTUS decision in 1954, it led to a movement away from evolving democratic ideals by the "Dixiecrats" in the US House and Senate from those former Confederate states as they began to become more and more disgruntled with their own party's stance on segregation and equal rights based on race. It became a full-scale juxtaposition once LBJ championed and managed to get the 24th amendment and the Civil Rights Act of 1964 enacted. Once that took place, the "Solid South" quickly changed in color from blue to red and has remained relatively that way ever since. Presidential elections have been won and lost based on this conservative/liberal flip-flop that took place between the two parties. It was a sweeping and fundamentally total reversal in the philosophies of both parties.
However, this election cycle is a bit of an aberration. While I don't think it can be argued that the democrats, thanks (or no thanks, depending on your viewpoint) largely to the strength and breadth of the Bernie Sanders campaign, has moved (at least as far as the platform is concerned) the democratic agenda further to the left, the republicans seem to be relegating their evangelical base to somewhat secondary status while fully embracing Trump's tough-talking, in-your-face and politically-incorrect (by design) attitude against those whom his disciples would proclaim to be unequivocally wrong from a fundamental aspect and, some, downright enemies of the state. I certainly don't see Trump as a genuine conservative by any means. His elucidations on his proposed policies and the details in the manner in which he intends to carry them out is extremely vague to say the least. His talent is communicative....although a billionaire, he seems to have the innate ability to connect with who may be the most forgotten demographic group in America....the white, middle-class American male. His appeal to this segment of society is the bedrock of his success as a candidate and he's done a magnificent job of bringing them over to his side and reaching into their hearts and minds. In this context, his campaign takes on a much more populist demeanor than if he were simply a "God, Guns & Guts" old-style republican.
Both parties are in a state of flux right now. In my opinion, a third-party could possibly gain some traction (not this time though) and present a legitimate option to the pathetic choices with which the major parties have give us this time around. As always, it'll be about money so I'm not optimistic that a serious 3rd party can evolve. However, the present political climate is ideal to encourage such a development. God help us all.
