Senators, including Democrat Catherine Cortez Masto, raised questions as to whether President Donald Trump received due process in the House impeachment inquiry and brought up other constitutional issues Wednesday as the Senate began the question and answer phase of Trump’s impeachment trial.

Later in the evening, after Cortez Masto asked about Trump’s due process, fellow Democrat Jacky Rosen, with other senators, asked how Trump’s action to withhold military aid to Ukraine differed from other holds of foreign aid.

Both senators had planned to ask multiple questions, according to their offices. But it was unclear exactly when they would get a chance as Democratic leaders strove to ensure that their questions were pointed and avoided redundancy.

“Senator Cortez Masto has prepared a number of questions for the House managers and the President's counsel,” said her spokesman, Ryan King. “She believes that the House managers presented a strong case and she listened to the defense closely.”

“The senator believes the defense left a lot of unanswered questions and looks forward to offering questions to follow up on each side’s argument,” he said. “She continues to believe that the Senate must hold a full trial with all relevant evidence and witnesses included so she and the American people have all of the facts.”

On Twitter, Rosen posted a video of her question being asked and answered.

“I’m taking my constitutional duty in this trial seriously,” she wrote. “Today, I joined several colleagues in asking the House Managers how the President’s hold on the foreign assistance to Ukraine differs from other holds on foreign assistance.”

Wednesday was the first of two eight-hour sessions of questions. Under Senate impeachment rules, the senators sit at their desks, write down their questions and send them to Chief Justice John Roberts, who is presiding over the trial. Roberts reads the questions aloud and announces to which party they are addressed, either the seven House Democratic impeachment managers, the president’s lawyers or both. Each has five minutes to respond. When both parties are queried, they split the time.

In response to Cortez Masto’s question, Rep. Val Demings of Florida, one of the seven House impeachment managers, argued that Trump had opportunities to have his counsel represent him in the House investigation, but chose not to.

“President Trump was invited to attend and participate in all of the Judiciary Committee hearing,” Demings said, adding that they could have cross-examined witnesses, raise objections, present evidence and call his own witnesses.

“But President Trump refused,” she continued.

Trump’s lawyers have argued that the president’s due process rights were violated when his counsel was not included in closed-door depositions of 17 witnesses held by the House Intelligence Committee. They were not invited for subsequent public Intelligence Committee hearings where the deposed witnesses told their story. By the time the Judiciary Committee held hearings, Speaker Nancy Pelosi had already told the panel to draw up articles of impeachment.

Intelligence Committee Chairman Adam Schiff, the lead House impeachment manager, has said that the depositions were held behind closed doors in order to prevent witnesses from hearing one another’s stories, which could prevent the finding of facts.

The House Democrats’ impeachment case contends that Trump abused his office by withholding military aid to Ukraine, and a White House visit, to force the Ukrainian government to investigate former Vice President Joe Biden, a potential political rival for the presidency. They also contend he sought to cover up his alleged wrongdoing by not cooperating with the investigation.

In response to Rosen’s question, Rep. Jason Crow of Colorado, another House manager, said that the president's decision was not routine or typical of past presidents, including President Barack Obama.

“In the cases of Obama’s temporary holds, Congress was notified for the reasons for those holds,” Crow said.

He said the Ukraine affairs also differed from Trump’s other holds on foreign aid. He cited aid for Afghanistan withheld in March because of concerns about terrorism and Central America withheld in September because of immigration.

“They were done for reasons of official U.S. policy,” Crow continued. “All of this goes to show there is no legitimate policy reason.”

Trump has said he held up the funds over concern about corruption in Ukraine and not to force an inquiry into the Biden's. He's also said he wanted America's European allies to take on a larger share of the foreign-aid burden.

During the back and forth Wednesday, all eyes were on a group of Republican senators who have signaled that they may vote with Democrats for the Senate to subpoena witnesses and documents. Those include Sen. Susan Collins of Maine, Sen. Mitt Romney of Utah and Sen. Lisa Murkowski of Alaska.

Democrats, including Minority Leader Chuck Schumer, have pushed to get four Republicans to vote for witnesses. But Majority Leader Mitch McConnell, who wants a short trial, is expected to try to keep his Republicans unified against Democrats. A vote on witnesses and documents is expected Friday. A vote on acquittal could also come by week's end.