Democrats took the House of Representatives while Republicans held on to the Senate and even picked up a few seats. So what difference does it make?

For starters, Democratic House leader Nancy Pelosi will return to the speakership she lost in 2010 and she has made clear the top items that would be on her agenda, ranging from a campaign finance overhaul to legislation designed to reduce health care costs.

While she has been coy about how Democrats will use their new-found power to reign in the overreach by President Donald Trump, many of her senior aides are expected to unleash an onslaught of investigations that could cripple the Trump White House.

First off, the White House and federal agencies controlled by Trump’s appointees are about to find out just how unsettling scrutiny by House oversight committees can be. Democrats will control the agenda, and Trump’s entire administration is a target-rich environment, with scandal after scandal reported every week.

Ethical questions about foreign officials spending at Trump properties and questionable purchases and conflicts involving Cabinet officials have filled newspapers since his inauguration two years ago. Democrats intend to launch a number of other investigations neglected by Republicans who’ve been unwilling to conduct executive branch oversight and instead sought to insulate the president from his own Justice Department’s inquiry.

Topping the list is the investigation into Russia’s interference in the 2016 USA election being led by Robert S. Mueller III. No issue animates the Democrats more than the Mueller probe and the new majority party will struggle to contain calls for impeachment of Trump. Trump has already begun to confront Democrats by forcing resignation of Attorney General Jeff Sessions on and threatening counter-investigations of the Democrats. He said he’s going to be on a war-footing and this sets up what is likely to be a trench warfare for the rest of his term.

There’s a lot of concern that this is the first step towards derailing the Mueller probe, which could lead to a constitutional crisis and an impeachment hearing. Democrats’ first step if the investigation is shut would be to preserve evidence Mueller has collected so that the Trump administration doesn’t hide the files. With their new House majority, the Democrats could bypass the Trump Justice Department by subpoenaing Mueller to get information. The Democrats could then move the probe under the jurisdiction of a congressional committee and hire Mueller to see it through with full subpoena power.

Of course, Republicans still control the Senate, so even if the House moves to impeach Trump, which requires a simple majority, conviction in the Senate would require a two-thirds majority. That seems pretty unlikely. Still, even if he survives impeachment, Trump will now have a check on his dictatorial tendencies. Mueller might also turn over his evidence to local law enforcement jurisdictions — in New York — where alleged crimes were committed.

Meanwhile, Trump’s legislative agenda is dead for all intents and purposes. Congress couldn’t get much done when Republicans controlled all the three branches of government, so the odds on any accomplishment over the next two years are almost nil.

Any bill that gets through the House or Senate can be blocked in the other. This may suit Trump just fine since he will try to blame the Democratic House for nothing getting done, which could become a theme for the presidential election two years from now. But he was already blaming them anyway despite the total control of the government by the Republicans.

Heading to the next presidential election, Trump may be feeling edgy after being rebuked by suburban voters across the nation. Democrats took the House because of gains in affluent, well-educated suburban districts, and voters who didn’t like Trump are likely to change their minds if he’s on the ballot in 2020.

The Democrat win of more than 35 seat majority over the Republicans is more impressive than even 12 years ago when they similarly took the House by capitalising on President George W Bush’s disastrous response to Hurricane Katrina. They went on to win both the Senate and the White House in 2008, a prospect that is increasingly looking likely in what would be a slugfest in 2020.

The Democrat win of the House was only limited by the fact most of the congressional districts are currently drawn in favour of the Republicans. But since Democrats also took control of seven more governorships and state legislatures in this election, there is a chance for them to redraw those congressional maps going forward to even out the discrepancies in a way that would allow the Democrats to pick up more seats.