A key committee of the US House of Representatives voted along party lines on Friday to approve two articles of impeachment against Donald Trump, charging the president with abuse of power and obstruction of Congress.The action by the Judiciary Committee sets up a historic vote next week in the full House that could make President Trump only the third president in US history to be impeached.Democrats who control the House accuse the president of betraying the public trust by withholding $391m in military aid to pressure Ukraine President Volodymyr Zelenskyy to announce an investigation of former Vice President Joe Biden, one of Trump's top political rivals.Democrats cited evidence produced in a three-month investigation by the Intelligence Committee into allegations by a whistle-blower that Trump sought a promise from Zelenskyy to investigate Biden in a July 25 telephone call. Trump also wanted an investigation of a discredited narrative promoted by Russia that it was Ukraine that hacked the US elections in 2016.Unanswered questionsThe Intelligence Committee held public hearings with 12 witnesses and produced text messages and emails showing Trump and key administration officials pressured Zelenskyy to announce the politically motivated investigations.Nine administration officials refused to comply with House requests to testify, complying with orders from Trump and White House lawyers not to cooperate with the impeachment inquiry.Instead of pursuing enforcement of subpoenas for testimony in federal court, House Democratic leaders decided to move forward quickly with the articles of impeachment leaving a number of unanswered questions.The speed of House action has opened Democrats to criticism they are treating Trump unfairly by failing to assemble an undisputed set of facts to support the allegations Trump orchestrated a pressure campaign in Ukraine.Democrats, however, have already won several lower-court rulings upholding congressional subpoenas in other investigations, proceedings that have taken up to eight months are still subject to appeals by Trump. Reasonable within authorityRepublicans argued a higher level of proof is required to charge the president with any criminal offence and accused the Democrats of putting forward a nebulous, ambiguous charge of abuse of power."No abuse of power ever took place and there certainly isn't enough support here in the evidence presented," said Republican Steve Chabot.During more than 12 hours of debate in the House Judiciary Committee on Thursday, Republicans sought to position Trump's actions as reasonable within his authority to advance US anti-corruption policy in Ukraine, a notoriously corrupt country, they said.Democrats responded that the argument Trump was actually concerned about corruption is false, even "laughable", Representative David Cicilline said.READ | US president Donald Trump went on a Twitter tear and posted more than 60 times in 3 hours to rage about impeachment and the FBITrump never mentioned the word "corruption" in his phone call with Zelenskyy and the US Defense Department had already certified Ukraine met anti-corruption benchmarks, Cicilline said."We can argue about the facts all day long, but the facts are pretty clear. The president abused his power," said Democrat Val Demings.Public opinionTrump has claimed there was no "quid pro quo". Republicans pointed out that Zelenskyy has repeatedly said he felt no pressure from Trump.House Speaker Nancy Pelosi said on Thursday the full House will take up impeachment next week. If the House votes to impeachment Trump, a trial would be held in the Republican-led Senate.Senate Majority Leader Mitch McConnell said such a trial would be the chamber's "first order of business" in January. A conviction, which would remove Trump from office, is unlikely at this point.Editorial boards of major US newspapers USA Today, the Los Angeles Times, the Boston Globe and the Washington Post have concluded that there is sufficient evidence to impeach Trump.But American public opinion is split. A running average of polls of US public opinion compiled by RealClearPolitics.com suggests 47 percent of Americans say Trump should be impeached and removed from office, while 46 percent say he should not be impeached.