Woodrow Wilson lost 60, Warren Harding 77. Harry Truman lost 54, Lyndon Johnson 47. Ronald Reagan lost 26, Bill Clinton 54. And Barack Obama? He lost 63. Incumbent presidents almost always watch their party lose substantial numbers of House seats in their first midterm congressional elections. The exceptions are rare — about as rare as FDR (gained nine in 1934) and George W. Bush (gained eight in 2002) being in the same sentence.

So the question that lingers in every political discussion this year is a perplexing one: Will a president whose campaign broke every rule, and whose presidency breaks every rule, be able to break with tradition and hold the House and Senate, legislative chambers where he does not even command the full confidence and support of his own majority party?

On the answer to that question rest the destiny of the president’s wall along the Mexican border, the Trump infrastructure initiative, the status of Obamacare, perhaps the shape of the Supreme Court, almost surely the remainder of Trump’s term.

Seldom has so much ridden on midterm congressional elections. And seldom has the political world been so complex, contradictory, and contrary.

This time, as in 1938 — when Southern conservatives asserted their strength in the Democratic coalition and when prospects for far-reaching social legislation dimmed — the fate of the president, and of the broader political alignment in Washington depends on many moving parts. It depends, too, on turnout, which almost certainly will be low, around 35 or 40 percent and perhaps lower among Republicans if custom prevails and the party out of power is more energized than the party in the White House.

Here are some of the constituencies that may plan an outsized role:

Women. Supporters of Hilliary Clinton remain angry about the election of Trump and are likely to flock to the polls in greater numbers than they did in 2010 and 2014, when Barack Obama was in the White House. Democrats will target middle-age and older women.

Younger voters. Democrats will focus on this group as well, though perhaps more as an investment toward the 2020 presidential election than toward November’s midterms; these voters are notoriously uninterested in voting in non-presidential years. Many of the younger Democratic voters were supporters of Sen. Bernie Sanders and have no natural repository for their efforts in midterms. The Democrats’ best hope may be in finding candidates who hug the extremes of consensus politics, but the victory of centrist Conor Lamb last month in Pennsylvania suggests the Democrats’ political pros will lean away from the fringes.

Supporters of the Tea Party coalition, particularly gun owners. These voters may form a backlash against the anti-gun rallies that so inspire the younger voters (above). They are playing defense now, which may end up mobilizing them. A danger for Republicans, however, is that fiscal conservatives congenial to the Tea Party oppose the recent budget deal and may feel alienated.

Hispanics. Trump’s aggressive opposition to immigration, his recent remarks about the Dreamers and his devotion to the Mexican wall may make many voters in this diverse group vulnerable to Democratic entreaties.

Rural voters. The farther a voter lived from a metropolitan area, the more likely he or she was to vote for Trump two years ago. Rural voters have leaned Republican for some time—Nebraska, for example, has delivered a total of six electoral votes to a Democratic presidential candidate in the last 80 years, five of them coming in the Lyndon Johnson landslide of 1964-–so this is fertile GOP territory for Republicans.

Conservatives. This is a surprisingly tricky voter group. They’re not partial to Democrats but view Trump with suspicion.

There remain many uncertainties. Only time will tell.

David Shribman is executive editor of the Pittsburgh Press-Gazette.

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