What to look for as the midterms near

This year's vital midterm congressional elections finally are coming into focus.

We've known for some time that these contests were important; at stake is not only control of the two chambers on Capitol Hill but also the character and trajectory of the final two years of Donald Trump's presidential term.

But now we have some clarity about what this election is about, what the terms of engagement are and what the fulcrums of power are in the 470 separate races scattered about the country.

These elections increasingly are taking on a national profile, because the question of party control in the Senate and the House suddenly seems so important --- and so much in doubt.

Throw away all the predictions. The commentators cannot have any comprehensive vision of all the moving parts; if the conventional wisdom was so wrong in the one high-profile contest of 2016, dismissing Trump as a phenomenon but not a factor, then most assessments of these myriad races cannot be trusted.

But as they grow nearer, some factors stand out as critical:

• Impeachment. It remains very unlikely that Trump -- assailed on the left, embraced on the right -- will be removed from office before his term expires in January 2021. That doesn't matter. Impeachment is one of the principal themes of these midterm elections anyhow. Who said there was any logic to American politics?

First, let's dispel the end-of-days fantasy held by so many never-Trumpers. Absent some major developments or exceedingly damaging findings from the inquiry being conducted by Robert S. Mueller III, the removal of the president must be considered a dim possibility.

Take the three "even ifs": Even if the Democrats take control of the House; and even if they initiate an impeachment process; and even if the House votes to impeach the president, the removal of the president requires a two-thirds margin in the Senate, and it's never happened.

The only president who came close to being convicted in the Senate, Andrew Johnson, exactly 150 years ago, survived by a single vote.

But does that matter for this November? Not at all. Few Democrats will utter the word "impeachment," though the Democratic base is thinking impeachment. Perhaps just as important: The more the Democratic narrative includes, even subliminally, impeachment, the more that threat will motivate the Republicans and the Trump base.

A good analogue of this dynamic might lie in 1940s France, where Charles de Gaulle, in exile and desperate to rally Frenchmen to resistance, was barely a factor in metropolitan France ... until Vichy France condemned him to death. Then -- voila! -- he won immense favor and support. Threaten Trump with impeachment and his supporters will flock to the polls.

• The profile of the parties. Both of the major political parties are in transition. And how they appear on Nov. 6 will be a critical factor.

The Democrats are struggling to decide whether they ought to stride to the left (like congressional insurgents Ayanna Pressley, a Boston city councilwoman who defeated Rep. Michael Capuano, a 20-year veteran of the House, and Alexandria Ocasio-Cortez, a political newcomer, who upset Rep. Joseph Crowley of Queens and the Bronx) or hug the center (like Rep. Conor Lamb, who won a Pittsburgh-area congressional district that went for Trump less than two years earlier).

Meanwhile, the GOP is struggling to decide whether to stick with Trump, whose political style does not play well to suburban Republicans, or break with him, perhaps by criticizing his behavior but praising his policies, especially on the economy.

• The blue-collar vote. This was perhaps the most important, and least understood, swing vote in the presidential election that swept Trump into office and swept away many of the assumptions that animated American politics.

Trump appealed to -- and largely continues to appeal to -- blue-collar voters. Though labor families are a shrinking part of the American electorate, their voting behavior remains an intriguing phenomenon; Trump's performance among these voters, since the New Deal a reliable part of the Democratic coalition, matched that of Ronald Reagan in his 1984 re-election campaign. He also outperformed Reagan among white union members.

Related and just as important: Trump far outperformed former Gov. Mitt Romney of Massachusetts, the 2012 Republican nominee, among white women without college degrees.

This fall's congressional contests will test the fondest hope of those on the left -- that Trump's blue-collar supporters will awake from their reverie and realize that the president's policies, especially on trade and taxes, hurt the very blue-collar Americans who are his most ardent supporters -- or that his comportment -- all that talk about multiple extra-marital affairs followed by tawdry payoffs to former paramours -- will alienate the religious conservatives who supported him in 2016.

That's possible, but not likely. Many of these voters remain angry at the very elites who express these views (and these hopes). "There are a lot of Trump people who have been peeling away, particularly suburban women," Christopher Beem, managing director of the McCourtney Institute for Democracy at Penn State University, told me. "But there is a core group of supporters who say Trump upsets the right people; he makes angry the people we want to make angry. There's a group that just loves that he is rude and mean and combative and picks fights with the elites."

• The economy, stupid. Those three words got Bill Clinton elected in 1992 and have been the guiding philosophy of American elections for two generations. It is also the root hope of the Republicans and the White House. But what if it no longer applies?

"While economic distress may harm the party in power, economic strength might not help it as much as in the past," Michael J. Boskin, who was chairman of George H.W. Bush's Council of Economic Advisers, has argued. "As voters become wealthier, more have the luxury of focusing on other issues."

If that is so, the Republicans' best card may not have much potency. The latest Gallup Poll shows that only 12 percent of those surveyed believe the economy is the biggest issue facing the country. That low number may be a matter of pride and satisfaction for Republicans, but if Boskin is right, it should be a matter of worry as well. If voters focus on other issues, they are turning their gaze from the GOP's greatest strength.

David Shribman, a Pulitzer Prize winner in journalism, is executive editor of the Pittsburgh Post-Gazette.