Everywhere in American politics, there is upheaval, and at the centre is President Donald Trump.

This is the week Washington and the world will seek answers to some of the most vital and pressing questions prompted by Mr. Trump's ascendancy.

Some of the answers will come from State Department officials sorting through the details of a possible meeting between Mr. Trump and North Korea's Kim Jong-un. Some will come from administration trade officials deciding how, or whether, the Trump steel and aluminum tariffs will affect Canada and other American allies.

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And some will come from voters in the Pittsburgh suburbs, where a hard-fought congressional contest is racing to a bitter Tuesday finish, and where analysts will examine whether the resolution foretells the results of the midterm congressional elections eight months from now. These results might suggest the beginning of a blue Democratic wave that will peak in the presidential election year of 2020 – or indicate that the Trump base remains strong and loyal.

The answers to all three could be clear by week's end. But some others may linger for months, even years.

It may be left to historians to determine whether Mr. Trump's dedication to protectionism marks a signature departure from Republican orthodoxy. Or whether the President's ideology – if in fact he has one – represents a new recipe for the GOP, or is in actuality more showmanship than statesmanship.

To be sure, many of these issues have hovered over American politics for some time. But this is the first time they have converged – and the result is not a harmonic convergence in Washington. The capital craves ideological clarity and moves to rhythms that were established two generations ago that are in peril from a President who was not schooled in them, does not wish to learn them and has no respect for them.

The upheaval is prompted by a President nominated, and supported nominally, by a party whose calling card for 125 years generally has been predictability, steadiness, frugality and reverence for past patterns of behaviour. Mr. Trump embraces none of those characteristics and, in fact, contradicts most of them. Indeed, the only two major events of the Trump era that conform to even a modern, post-Reagan Republican outlook are his nomination of a conservative, Neil Gorsuch, to the Supreme Court, and his support for a tax cut.

But Mr. Trump's backing of a US$1.4-trillion tax cut was not accompanied by the sort of budget discipline Mr. Reagan espoused (and Democrats at the time deplored), and his determination to impose stiff new tariffs sets him apart from Republican free traders and into the cautious embrace of Democrats who, since 1982, have called for protective levies. Indeed, the Trump tumult is best viewed on the trade issue, in which many devoutly Democratic trade unionists, who generally deplored Mr. Trump as a candidate, support him on the steel and aluminum tariffs.

Although Mr. Trump has carved out a temporary tariff reprieve for Canada and Mexico, the implications for the Americans' two NAFTA partners will be examined this week when Robert Lighthizer, the U.S. chief trade negotiator, begins a fortnight-long evaluation of possible exemptions from the Trump levies. While Mr. Lighthizer has criticized past Canadian trade moves as "a massive attack on all of our trade laws," he is familiar to trade officials in Ottawa and with the trade profile and political circumstances in Canada.

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Then there is the Trump infrastructure initiative. It has scrambled the political calculus. The notion is congenial to Democrats (because of their links to construction unions and their general support of the economic stimulation large-scale spending programs bring) and anathema to many Republicans (who retain a skepticism of big government and big spending, particularly since many of the projects, and thus the government spending, likely will be in Democratic-leaning states).

But now, voices on the right worry the new levies on imported steel could raise the price of the infrastructure projects dramatically. One of the loudest, most important voices expressing skepticism of these tariffs: the United States Chamber of Commerce, traditionally a sturdy GOP ally.

"Trump is kind of a mash-up of elements of Republican history," said John Pitney Jr., a political scientist at California's Claremont McKenna College who often writes on Republican topics. "The protectionism is inconsistent with Reagan Republicanism, but is very consistent with 19th-century Republicanism. The flirtation with dictators and isolationism is, again, different from Reagan – but brings to mind Charles Lindbergh," a reference to the storied aviator who was decorated by Nazi Germany and became a leading voice for American isolationism before the 1941 attack on Pearl Harbor.

"In many ways," Mr. Pitney continued, "Trump is a combination of Republicanisms that many Republicans wanted to forget."

The coincidence that the latest special congressional race takes place in the centre of American steel country has only sharpened the attention on the contest. The two candidates are running to fill out the last months of a seat vacated by a Republican congressman, which makes it a modest prize at best. Its importance is lessened by the fact that the congressional district in which the Democrat Conor Lamb and the Republican Rick Saccone are running will not even exist when voters go to the polls in November for the midterm congressional election; the state is in the process of redrawing its electoral map.

Like so much in the Trump era, this is a contest more about symbolism than substance. And yet, it is receiving enormous nationwide attention, with Mr. Trump visiting the district on Saturday night and saying of Mr. Saccone, a state representative: "This guy can really help me." The result will matter less to the constituents of Pennsylvania's 18th congressional district than to the many, in politics and the media, who have invested the contest with outsized meaning.

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"If the Democrat wins, the Republicans will be very nervous about Trump's staying power," said Dennis Goldford, a political scientist at Drake University in Iowa. "If the Republican wins by double digits, it will put Republicans at ease. If it's a point or two either way, both sides will declare victory."