There has been a lot of debate in the US in the past few weeks about whether the presidential candidacy of Donald Trump should be taken seriously or treated as some elaborate sideshow to the main carnival yet to begin.

Those conversations will only grow in volume and importance now that the New York businessman has crossed a line held sacred by his fellow Republicans, by questioning the hero status of Senator John McCain. Trump had, of course, already faced heavy censure elsewhere for his comments on the criminality of Mexicans and other migrants, and for his hypocritical attacks on the Chinese custom that sustains many of his business interests.

The establishment-challenging rise of Trump on the right has been accompanied by the increasing prominence of Bernie Sanders as a far more left-leaning, even socialist, challenger to what has long-seemed an inexorable march to the Democratic nomination, and White House accommodations, for Hillary Clinton. For a counterpoint to Trump's criticism of his fellow conservatives' military record, see what might be considered Sanders' thoroughly un-American, and certainly very un-Clintonian, rejection of growth as the unchallenged economic priority of government.

It is difficult to remember two candidates so popular yet so obviously removed from the long-held consensus of their parties as Trump and Sanders.

Complicating matters further has been the emergence of Black Lives Matter as a potential political, rather than just social, force. This movement has built on the mounting dissatisfaction with persistent police brutality against African-Americans and the even more stubborn plague of Southern racist pride, as seen in recent waves of Confederate flag-waving and Klux Klux Klan rallying.

Earlier this week, Black Lives Matter supporters disrupted an event attended by Sanders and his fellow Democratic aspirant Martin O'Malley in what could be a sign of things to come for left-leaning candidates perhaps too accustomed to the tacit support of the black community.

These factors have led to a somewhat disorientating phase in the American political cycle, with new voices and new (or merely forgotten) concerns often dominating the discourse. Could these new preoccupations even explain the unusually muted response among the media, politicians and public to the killing of five military personnel by what many speculate was an Islamic extremist gunman in Chattanooga last week? While there has certainly been sorrow and condemnation, the attention on these attacks has not approached the level attached to past violence of this nature in the post-September 11 world, either at home or abroad.

What are the ramifications for the 2016 presidential campaign?

For all the weight that has been attached to the impressive crowds and polling results Trump and Sanders have attracted so far, the most likely outcome still appears to be for the primaries process to turn out two thoroughly establishment candidates, as it has reliably done in years past. Nonetheless, the concerns brought to the surface by the two outliers could still have a significant impact on the public debate and on the contest between the eventual candidates. So too could the newly empowered black rights movement.

Immigration has long been a hot political topic, with many Democrats and some sympathetic Republicans pushing for significant reform aimed at increasing paths to legal permanent residency and citizenship for those in the country illegally. The vein of resentment towards migration that Trump has tapped could further frustrate these efforts, and convince its proponents to not bother pursuing it.

In the case of Sanders, it seems likely that some ideas, such as breaking up the big banks deemed 'too big to fail' in the aftermath of the 2008 financial crisis, might prove too utopian to gain middle-ground currency. His anti-Wall Street streak, could, however, at least hold Clinton's feet to the fire during the upcoming campaigning and debate season. The former Secretary of State has already been noted to have moved to the left on economic matters in recent speeches.

Meanwhile, any further growth in the Black Lives Matter movement could help transform popular dissent into increased voter turnout among African-Americans. This could, in turn, lead to increased questioning of candidates as to how they would respond to the growing demands of the new bloc. If so, it would be something of a perverse development, just as the country's first black president leaves office.

Of course, we are only at the beginning of the election process. Incredibly, there is still over a year for candidates and the voting public to determine what previously marginal views will join the consensus of both sides of politics. Then comes the even more difficult project of attempting to forge a middle path between them.