There’s a wise adage warning against wrestling with pigs: You just both end up covered in mud, and he loves it.

That’s the trap Hawaii U.S. Sen. Mazie Hirono and many Democrats are falling into as they battle the helter-skelter presidency of Donald Trump.

By resorting to broadside personal attacks like Hirono made last week against Attorney General William Barr at a hearing on the Mueller report, Democrats play Trump’s game of theatrics and name-calling, which they can’t win because he’s so much better at it than they are.

Instead of wrestling him for the low road, their best shot at prevailing is behaving like the adults in the room with a more businesslike approach to seeking accountability and greater focus on substantive policies that address voter needs.

Hirono cited fair concerns about the attorney general’s handling of special counsel Robert Mueller’s report on Russian interference in the 2016 election and alleged obstruction by Trump.

But her points were lost in a rambling statement in which she compared Barr to Rudy Giuliani and Kellyanne Conway, called Trump a “grifter and liar” and re-litigated old business from Barr’s confirmation hearing to the 1989 arrest of Manuel Noriega.

This is a losing look for Democrats, feeding into the GOP narrative that the Russia inquiries are more about politics than oversight. The personal rancor gives cover to Barr and others as they ignore subpoenas from the Democratic-controlled House.

Democrats billed their takeover of the House last year as a chance to prove they could govern effectively. They promised a stream of legislation on economic equity, health care, climate and other major concerns.

It hasn’t materialized as they’ve become increasingly paralyzed by infighting, culture wars and legal battles with Trump.

Trump would love to keep it that way for the next 18 months before the 2020 presidential election. He thrives on chaos and is happy to distract attention from his relentless rollback of regulatory checks on economic predators and polluters.

Reports from the presidential campaign trail indicate that only the die-hard bases of either party are asking much about Washington subpoenas and investigations.

Voters who can still be swayed, and will decide the election, want to know how the candidates will help their families and communities and improve their lives.

Democrats in Congress certainly must work to hold Trump accountable for any misdeeds and defend their constitutional authority to provide oversight of the administration.

But they need to be more professional and disciplined about it, stop getting sucked into Trump’s vortex of endless drama and regain their focus on policy goals.

Lawmakers like Hirono must decide whether it’s more important to thump their chests and throw red meat to the party’s base or give themselves a chance to win the 2020 election.

Reach David Shapiro at volcanicash@gmail.com.