RUTHFULLY YOURS

Mr. Trump’s tax returns and foreign business dealings will get frequent star turns. Democrats think they can prove Mr. Trump has exploited his office for personal enrichment, or in some way that matters to Robert Mueller’s Russia investigation. If not, at least they’ll embarrass the Trump family. Ivanka and Jared should prepare for subpoenas and dives into their email habits and security clearances.

Democrats will also run investigations into payments to Stormy Daniels; the Administration’s policy of separating children at the border; and every consultation with a business about a deregulatory decision. House Democrats will trail every cabinet officer down to whether he ordered a cocktail on a commercial flight. This will present even greater problems in staffing federal agencies.

On policy, Mrs. Pelosi owes her speakership to the left and she will tilt that way. She is already facing a revolt on the left over a rules change to impose pay-as-you-go budgeting. Liberals think it will hamstring their spending plans. That’s fine with us since Paygo, as it’s known, was always more political eyewash than genuine fiscal restraint.

The real House tension will be between the new socialist vanguard and the 30 or so Democrats who won in GOP-leaning districts. It will be instructive to see how many defect from the Green New Deal or Medicare for All if Mrs. Pelosi dares to bring those to the floor.

One certainty is the end of pro-growth legislation. The trend will be toward higher taxes, more regulation and more harassment of business. The new House rules have already cashiered “dynamic scoring” that forced the Congressional Budget Office to think about how a proposal affects the economy. Dynamic scoring isn’t some GOP effort to prove taxes “pay for themselves” but a tool that informs lawmakers of economic costs and trade-offs and can improve policy.

The GOP Senate, with a new majority of 53, should be able to check the left’s impulses to jack up the corporate tax rate or restore the federal deduction on all state and local taxes. Mrs. Pelosi will try to lure Mr. Trump into a deal on infrastructure or drug prices. But Mr. Trump will be less likely to go along if he has to rely on the GOP to fend off impeachment.

It’d be nice to think there’s a chance at cooperation on immigration, but it’s unlikely as long as Democrats think the issue gives them an edge in elections. It’s clear from the shutdown over “border security” that Democrats think they have the edge on immigration, even if collateral damage could be the young adult “Dreamers” who need legal clarity to stay in the country.

The best test of Mrs. Pelosi’s deal-making sincerity will be what she does on Mr. Trump’s new Nafta deal. The President went a long way in negotiations to appease unions, with Ohio Sen. Sherrod Brown as Big Labor’s whisperer, but the President still doesn’t have the votes. When she took the gavel in 2007, Mrs. Pelosi stuck George Bush’s pending trade deals in a drawer.

All of this will unfold along with the fight for the 2020 Democratic presidential nomination, which will reinforce the party’s anti-Trump fervor. Voters may think they sent Democrats to Washington to “check” Mr. Trump’s unpresidential habits. Americans may soon discover that they’ve invested those hopes in more polarization and vitriol.