It's been less than two weeks since US House Speaker Nancy Pelosi announced an impeachment inquiry into President Donald Trump, but the investigation has dominated the US political scene and the presidential agenda. The inquiry focuses on Mr Trump's call with Ukrainian President Volodymyr Zelenskiy on July 25 in which the US President said "I would like you to do us a favour though," as he urged Mr Zelenskiy to launch a corruption investigation into his political opponent, former US vice president Joe Biden, who is seeking the Democratic nomination. Paul Rosenzweig, a legal expert at R Street institute and a former deputy assistant secretary for policy at the Department of Homeland Security, said there was a clear case for impeachment. "President Trump is essentially daring the democrats to impeach him. If they fail [to impeach him in the House], he will be able to establish a presidential norm that it is acceptable to use his powers to solicit information from a foreign government," Mr Rosenzweig told <em>The National.</em> Since the announcement, Mr Trump has been on the attack, tweeting no less than 300 times about the impeachment attempt, and borrowing from his lines in the Mueller probe in calling it a “witch-hunt” and “presidential harassment”. But unlike the Mueller probe, which mostly involved Mr Trump's campaign aides and not the president directly, Mr Rosenzweig said the impeachment case "is very clear" in that the US president is promising the Ukrainian leader "money for dirt on my opponent". The money in this case is US military equipment, but Mr Trump denies any “quid pro quo”. “He is not just seeking assistance from a foreign government, but he is also giving them leverage in US politics,” Mr Rosenzweig argued. Three House committees have already issued subpoenas to US Secretary of State Mike Pompeo, five of his aides, Mr Trump’s lawyer Rudy Giuliani and the White House. The investigation also involves the vice president's office. Former US envoy to Ukraine Kurt Volker, who resigned after the inquiry, has already testified in Congress and provided details that include text messages on Mr Giuliani's involvement in bargaining with the Ukrainian government. Mr Giuliani fired back and tweeted his own text exchanges. “Unlike [former President] Richard Nixon who kept interference to a small circle of aides around him, Mr Trump has involved a large number whose names we see getting dragged into the investigation,” Mr Rosenzweig argued. <br/> Although Democrats have enough votes in the House to impeach Mr Trump, it is still unlikely that they can garner two-thirds of support in the Republican-majority Senate to oust the president. So far, Republican Senators Mitt Romney and Ben Sasse are the only two voices criticising the president from within his party. Mr Rosenzweig expected other Senators such as Susan Collins or Cory Gardner, who are up for re-election, to vote against Mr Trump, but still without reaching 67, the magic number required to convict the president. Mr Romney on Friday criticised Mr Trump's call for China and Ukraine to investigate the Biden family. A USA Today poll found that 45 per cent of Americans support impeaching Mr Trump while 38 per cent are opposed to it. The process is already distracting Mr Trump from other issues. His Twitter timeline is flooded with attacks on Democrats, and most of his press availability, even with foreign dignitaries, has been solely focused on the inquiry. Mr Pompeo has also taken a combative role in challenging the inquiry, accusing Democrats of harrassing State Department employees by asking for documents relating to the inquiry. "The US president is certainly distracted, and that would undermine him if he had to face a crisis [such as a new Iranian attack]," said Andrew Bishop, the head of research at Signum Global Advisers. But the US government bureaucracy is still functioning he explained, and "emails aren’t going unanswered any more than they were before". Mr Bishop told <em>The National </em>that Donald Trump's "growing domestic woes make him ever more eager for a win on the international front". Such a victory would be in the form of a diplomatic deal but not a military confrontation, he said. The problem, however, is Mr Trump's "adversaries might not be inclined to give him one …That applies to China, Iran and North Korea – all of whom are playing hardball with the US President," said Mr Bishop. The impeachment process is expected to intensify in the coming two months with a vote in the House expected before the end of the year. Several sources said the Democratic leadership in Congress wants to avoid dragging the process into the election primaries that start in Iowa on February 3.