President Donald Trump’s impeachment trial shifted swiftly to pointed, back-and-forth questioning Wednesday as Republicans strained to contain the fallout over John Bolton’s forthcoming book, which threatens their hopes of ending the trial with a quick acquittal.

The day started simply enough. Three Republican senators asked Trump’s legal team: If there was more than one motive for Trump’s conduct in Ukraine, as he pushed for political investigations of Joe Biden, should the Senate still consider the Biden pressure an abuse of power?

White House lawyer Pat Philbin responded there’s nothing wrong with the president acting on a personal as well as national interest. He declared the charge against Trump “absurd.”

Democratic Leader Chuck Schumer sparked lively debate asking whether the Senate could really render a fair verdict without calling Bolton or acting White House Chief of Staff Mick Mulvaney to testify.

“There’s no way to have a fair trial without witnesses,” responded Rep. Adam Schiff, the Democrat leading the prosecution for the House.

“Don’t wait for the book. Don’t wait ’til March 17, when it is in black and white to find out the answer to your question,” Schiff told the Senate.

The question-and-answer session, which began at 1 p.m. on Wednesday and will finish up Thursday, allows lawyers on both sides to make their final points before the senators vote on whether to hear witnesses and, eventually, on whether to convict the president and remove him from office.

Watch day 9 of the Trump impeachment trial here.

The uncertainty about witnesses arises days before crucial votes on the issue. In a Senate split 53-47 in favor of Republicans, at least four GOP senators must join all Democrats to reach the 51 votes required to call witnesses, decide whom to call or do nearly anything else in the trial.

»Meet the senators who hold Donald Trump’s presidency in their hands

Several GOP senators are reportedly undecided on whether to allow witness testimony in President Trump's impeachment trial. They are: Mitt Romney, Utah Susan Collins, Maine Lisa Murkowski, Alaska Pat Toomey, Pennsylvania Rob Portman, Ohio Jerry Moran, Kansas Cory Gardner, Colorado Lamar Alexander, Tennessee Prosecutors and defenders in Trump's trial have finished their opening arguments. Senators will now begin deliberations, submit written questions, and decide on President Trump's fate.

Senators must submit their questions to Chief Justice John Roberts. He will then read them and request an answer.

Senators must direct their question to either the House impeachment managers or the White House lawyers, not both, and senators cannot ask each other questions. Senators also cannot respond after their questions are answered.

The process keeps the senators silent, like a jury, as they decide whether to vote to convict the president.

John Roberts serves as the 17th Chief Justice of the United States. He was born in Buffalo, N.Y., and grew up in the Midwest. He completed his undergraduate degree at Harvard and then attended Harvard Law School, graduating with a law degree in 1979. Roberts worked as a clerk during his early legal career, then went into private practice, arguing 39 cases before the Supreme Court. Roberts was appointed to the U.S. Court of Appeals in 2003. President George W. Bush nominated Roberts to the Supreme Court af

When a senator has a question, a Senate page is expected to take the piece of paper from their desk to Roberts’ seat at the head of the Senate. The senator must sign the piece of paper.

Senate Majority Leader Mitch McConnell said Tuesday that the questions would alternate between Republicans and Democrats.

Here are the key figures in President Donald Trump's impeachment trial. House Speaker Nancy Pelosi. She led the impeachment effort. Chief Justice John Roberts. He will preside over the trial. The Senate's political leaders - Majority Leader Mitch McConnell and Minority Leader Chuck Schumer. The president's legal defense team - White House counsel Pat Cipollone, Trump personal lawyer Jay Sekulow, Kenneth W. Starr, Alan Dershowitz, along with Robert Ray and Jane Raskin. House Democratic impeachment managers

Senators on both sides have been coordinating with their leaders to avoid duplicate questions. U.S. Sen. Kevin Cramer (R-N.D.) said he’d been given a form on which to list his questions, U.S. Sen. Dick Durbin (D-Ill.) said he’d given his questions to Senate Democratic leader Chuck Schumer’s office, just so they could figure out the “sequencing and avoiding duplication.”

Durbin said that when he asked a question during the impeachment trial of President Bill Clinton, "it turned out six other people had the same idea. So we all joined in one question, and it was attributed to all of us."

President Bill Clinton was impeached on perjury and obstruction of Congress charges on Dec. 19, 1998. He was acquitted by the Senate on Feb. 12, 1999. Fourteen senators from that trial still remain in office. Here's how they voted. Susan Collins, R-Maine. Not guilty on both counts Michael D. Crapo, R-Idaho. Guilty on both counts Richard Durbin, D-Illinois. Not guilty on both counts Mike Enzi, R-Wyoming. Guilty on both counts Dianne Feinstein, D-California. Not guilty on both counts Charles Grassley, R-Iow

Senators have up to 16 hours to ask questions, as they did in Clinton’s trial. That should break down into two eight-hour days, with senators taking breaks after every 10 or 12 questions.

There is no official time limit for House impeachment managers or White House lawyers to respond, but both McConnell and Roberts urged brevity.

“During the question period of the Clinton trial, senators were thoughtful and brief with their questions, and the managers and counsel were succinct in their answers,” McConnell said Tuesday. “I hope we can follow both of these examples.”

»What are articles of impeachment all about?

Roberts asked the two sides to limit their answers to five minutes each. He noted that transcripts from the Clinton trial show that a similar request by Chief Justice William Rehnquist was met with laughter from within the chamber.

“Nonetheless, managers and counsel generally limited their responses accordingly,” Roberts said.

Republican and Democratic senators will doubtless ask friendly questions to their managers and also use questions to poke holes in the others' arguments.

The U.S. House formally sent President Donald Trump's impeachment articles to the Senate on Jan. 15, 2020. House Speaker Nancy Pelosi first announced seven impeachment managers. The House then voted, along party lines, to transmit the impeachment articles across the aisle. Pelosi signed the House's order, then gave fellow Democrats souvenir pens for the occasion. The impeachment managers, along with Capitol clerical personnel, then marched over to the Senate. Trump has been charged with abuse of power

The U.S. Constitution requires a two-thirds majority in the Senate, or 67 senators, to convict in an impeachment trial.

Republicans hold 53 seats in the Senate, while Democrats hold 45. However, two Independents — including presidential candidate Bernie Sanders of Vermont — regularly caucus with Democrats, giving the nation’s blue party 47 votes.

If the Senate votes along party lines regarding impeachment — as did the House — 20 Republican senators would have to join Democrats in convicting Trump and removing him from office.

U.S. House Democrats have drafted two articles of impeachment against President Donald Trump. House leaders are charging the president with abuse of power and obstruction of Congress. They announced the articles of impeachment on Dec. 10, 2019. A full House impeachment vote could come before Christmas. If passed, the president would face a Senate trial in 2020, a presidential election year.

The first article of impeachment passed by the House charges Trump with abuse of power.

Democrats allege Trump “solicited the interference of a foreign government, Ukraine, in the 2020 U.S. presidential election. He did so through a scheme or course of conduct that included soliciting the government of Ukraine to publicly announce investigations that would benefit his reelection, harm the election prospects of a political opponent, and influence the 2020 U.S. president election to his advantage.”

»Read the best lines from President Trump’s Senate impeachment trial

The “election prospects of a political opponent” refer to Biden, currently a front-runner in a narrowing field of Democratic White House hopefuls.

The president “also sought to pressure the government of Ukraine to take these steps by conditioning official U.S. government acts of significant value to Ukraine on its public announcement of investigations.”

Democrats argue the president “used the powers of his presidency in a manner that compromised the national security of the United States and undermined the integrity of the United States democratic process. He thus ignored and injured the interests of the nation.”

How is your senator trending on impeachment?