C’mon, Obama. Get in the Game.

(Bloomberg Opinion) -- To the annoyance of many Democrats, former President Barack Obama has largely floated above the political fray instead of actively leading the anti-Trump brigade. He’s told associates that he doesn’t want to aggravate political polarization and wants to preserve his credibility by speaking out only selectively and on key occasions.

If that’s the case, now is such a time.

He doesn’t need to sound the alarm about President Donald Trump’s bad policies and vicious behavior. Others are doing that.

Instead, it’s the right moment for Obama to lay down a marker for Democrats, subtly warning against moving to extremes in response to Trump. Liberals, he thinks, need to “mix idealism with practicality,” according to an article last month in New York magazine.

Actually, in this political season, mainstream Democrats have done well in contested primaries. A New York congressional contest last month in which a young socialist defeated a Democratic House leader has been widely and wrongly over-interpreted by both opponents and enthusiasts as a sign that Democrats are veering left.

But Democrats are making some mistakes that Obama could help correct. In response to Trump’s policy of separating immigrant children from their families, politicians including Senators Kirsten Gillibrand of New York and Elizabeth Warren of Massachusetts have called for eliminating the Immigration and Customs Enforcement agency. Trump relishes that debate, which deflects attention from his abuse of children. There’s also pressure on Democrats to insist that the only way to improve the health-care system is to turn it over to the government, and to demand Trump’s impeachment now.

Obama could make his presence felt as midterm congressional elections approach by pushing back without picking fights. He could call for building on the Affordable Care Act, his signature health-care measure, instead of scrapping it in favor of a single-payer system. He could recommend letting the investigations of Trump by special counsel Robert Mueller and others play out before considering impeachment. He could urge that the focus on immigration issues be redirected toward helping children and families instead of fear-mongering. And by his calm example he could remind allies to respect civility even in turbulent times.

The 44th president’s standing is such that he’d provide some cover for Democratic candidates who are being pressured by the party’s left wing on these issues.

He’s the only one who possibly can reach younger voters, angry activists and suburban women simultaneously. Bill and Hillary Clinton have lost credibility; Warren doesn’t want to alienate the left; House Speaker Nancy Pelosi is worrying about holding on to her leadership job if Democrats take the House of Representatives, and Senate Minority Leader Charles Schumer wouldn’t be taken seriously by these constituencies.

It’s a mistake for Obama to ignore the elements in his party who believe, as the historian Sean Wilentz has written, that “the only way to fight right-wing populism is with left-wing populism.”

Trump is losing the border war politically, so when critics attack an enforcement agency instead of the policymaker, it plays into his hands. Likewise, Republicans are on the defensive on the big health-care issues, having misled the country for eight years in their assault against universal health insurance and having turned to a president who cares little about the topic. Changing the subject to debating the merits of what would be an immensely complicated, expensive and controversial single-payer system throws these Republicans a life raft.

In the era of Trump, another canard is that only shrill voices are heard. Over the past eight months, the three biggest Democratic winners, Alabama Senator Doug Jones, Virginia Governor Ralph Northam and Pennsylvania Representative Conor Lamb, all are moderate in manner as well as politics. Two Democratic incumbent senators in states Trump carried, Bob Casey of Pennsylvania and Sherrod Brown of Ohio, are known by colleagues as nice guys. They’re both likely to win by double digits this November.

There are others, however, whom the popular Obama might assist. He’s vowed to help the Democrats’ redistricting campaign, which seeks to reverse some of the huge gains Republicans scored in creating partisan congressional and state legislative lines after the 2010 census. Democrats were asleep at the switch then, when Obama was president and leader of his party. He also plans to selectively campaign for a few Senate candidates.

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