The House Judiciary Committee’s impeachment hearing on Wednesday marks a new phase in the investigation, as Democrats prepare to finalize their case against President Donald Trump, amid increased resistance from Republicans and the White House.

The proceedings will be led by Judiciary Chairman Jerrold Nadler, D-NY, whose committee is in charge of drawing up articles of impeachment against the president and sending them to the House floor for a final vote.

Neither Trump nor his lawyers will be present Wednesday, but it remains unclear whether the coming weeks could feature a direct confrontation between Democrats and the White House. Under the House rules, the president does have the right to participate in the Judiciary Committee hearings.

Nadler is now in control

Nadler is taking charge of the impeachment investigation from House Intelligence Committee Chairman Adam Schiff, D-Calif., who led the public hearings last month. The Intelligence panel investigation focused on whether Trump abused his power by pressuring Ukraine to investigate former Vice President Joe Biden, a leading 2020 Democratic presidential candidate. A report on its findings was released Tuesday. It is expected to be approved and sent to Judiciary on Tuesday evening.

Once Nadler has the report, Democrats will formally begin weighing whether there’s enough evidence to conclude that Trump committed an impeachable offense. Democrats must also decide whether to focus only on Trump’s actions with regards to Ukraine, or expand the list of potential articles of impeachment to include other matters.

Unlike Schiff, Nadler has a long history with Trump that predates the president’s political rise. The veteran House lawmaker represents parts of Manhattan and Brooklyn — Trump’s home turf — and has clashed repeatedly with Trump in the past, over real estate projects in New York City.

What is an impeachable offense?

The framers of the Constitution outlined impeachable offenses in broad terms, leaving it up to future lawmakers to decide on a case-by-case basis when to remove a president from office. The purpose of Wednesday’s hearing is to define which, if any, of Trump’s actions rise to the level of impeachable. Republicans took a similar step at this point in their impeachment investigation into President Bill Clinton in the late 1990s.

Lawmakers will hear testimony Wednesday from four legal scholars: Harvard Law professor Noah Feldman, Stanford Law professor Pam Karlan, University of North Carolina Law professor Michael Gerhardt, and George Washington Law professor Jonathan Turley. Turley also testified before the House in the Clinton impeachment.

Turley is the lone witness called by Republicans. GOP lawmakers have frequently criticized the impeachment investigation, and Rep. Doug Collins, R-Ga., the top Republican on the Judiciary Committee, attacked the process in a letter Monday to Nadler.

The Democrats’ dilemma

House Democrats still have to decide whether to focus exclusively on Ukraine, or go after Trump on a broader range of issues — a dilemma Democrats have struggled with since formally launching the impeachment inquiry in September.

Should Democrats decide to broaden their case against Trump, they’d likely focus on Mueller’s special counsel investigation into Russian meddling in the 2016 election and ties to the Trump campaign. In his final report, Mueller did not draw a conclusion about whether Trump obstructed justice. But Mueller pointed out ten instances where there was evidence the president or his associates tried to interfere with the probe.

If Democrats focus on the special counsel probe Wednesday, it could signal they are leaning towards adding obstruction of justice from that investigation to the list of articles of impeachment. That approach could open Democrats up to criticism that they are still fixated on the Mueller investigation, and bolster Trump’s claim that the impeachment is politically motivated.

Will the White House participate?

White House counsel Pat Cipollone announced Sunday in a letter to Nadler that the White House would not participate in Wednesday’s hearing. Cipollone slammed the investigation as a “baseless and highly partisan inquiry” that was unfair to Trump.

But that doesn’t mean the White House will refuse to cooperate in subsequent hearings. Under the impeachment rules passed by Democrats last month, the White House can participate in Judiciary Committee hearings, including cross-examining witnesses. The White House has until Friday to decide whether to attend the hearings.

What happens next

Nadler hasn’t announced more hearings beyond Wednesday, but the Judiciary Committee is expected to hold more in the coming weeks. The panel could also vote as soon as next week to draft articles of impeachment. If the committee approves articles of impeachment, they would move to the floor for a House vote. (An alternative would be passing a resolution to censure Trump, if Democrats decide not to pursue impeachment. A censure vote does not remove a president from office and is defined by the Senate as a “formal statement of disapproval.”)

Democrats have signalled a desire to wrap up the process by the end of the year. Congress breaks for its winter recess before Christmas. If the House sticks with its schedule, it has only three more weeks to vote on impeachment and send it to the Senate for a trial early next year.