The Republican-controlled U.S. Senate blocked Democratic attempts on Tuesday to obtain evidence and call a witness in U.S. President Donald Trump's impeachment trial, an early sign the proceeding could advance on lines favorable to Trump. 

Senators voted along party lines, 53-47, to block several separate motions from Democratic leader Chuck Schumer to subpoena records and documents from the White House, the State Department, the Defense Department, and the Office of Management and Budget related to Trump's dealings with Ukraine. 

Senators also rejected by the same tally a request for a subpoena seeking the testimony of acting White House Chief of Staff Mick Mulvaney. 

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Democrats have called on the Senate to remove Trump from office for pressuring Ukraine to investigate former Democratic Vice President Joe Biden, a political rival, and then impeding the inquiry into the matter.

Trump, who was impeached last month by the Democratic-led House of Representatives on charges of abusing power and obstructing Congress, denies any wrongdoing and describes his impeachment as a partisan hoax to derail his 2020 re-election effort. 

During early debate, Trump's chief legal defender attacked the case as baseless and a top Democratic lawmaker said there was "overwhelming" evidence of wrongdoing. 

With the television cameras rolling, U.S. Chief Justice John Roberts convened the proceedings and the two sides began squabbling over Senate Majority Leader Mitch McConnell's proposed rules for the trial. 

White House counsel Pat Cipollone, who is leading Trump's defense, attacked the foundation of the charges against the Republican president and said Democrats had not come close to meeting the U.S. Constitution's standard for impeachment. 

"The only conclusion will be that the president has done absolutely nothing wrong," Cipollone said as he argued in favor of McConnell's proposal to decide on whether to allow further witnesses or documents later in the trial. 

Democratic Representative Adam Schiff, who helped spearhead the House impeachment inquiry, summarized the charges against Trump and said the president had committed "constitutional misconduct justifying impeachment." 

Schiff said that although the evidence against Trump was "already overwhelming," further witness testimony was necessary to show the full scope of the misconduct by the president and those around him.

Democrats want a number of current and former Trump administration officials, including Trump's former National Security Advisor John Bolton, to testify. 

"For all of the name-calling and finger-pointing from the president's counsel, we did not hear a single argument on the merits about why there should not be the documents and witnesses we requested in this trial," Schumer said. 

Republican senators have not ruled out the possibility of further witness testimony and evidence, with likely votes later in the trial after days of opening arguments and senators' questions. 

McConnell unveiled a plan on Monday for what would be a potentially quick trial without new testimony or evidence. It would have given Democratic prosecutors and Trump's lawyers 48 hours, evenly split, to present their arguments over four days. 

That plan was changed to give each side three days to give opening arguments. The rules also will allow the House's record of the impeachment probe to be admitted as evidence in the trial, as Democrats had demanded. 

Democrats had accused McConnell of trying to rig a trial with proposed rules they said would prevent witnesses from testifying and bar evidence gathered by investigators. 

Trump was impeached on December 18 by the House of Representatives, and formally charged on the floor of the Senate last week with abuse of power and obstruction of Congress. It is only the third time a U.S. president has endured an impeachment trial, after Bill Clinton in 1999 and Andrew Johnson in 1868.  

Like his two predecessors, Trump looks almost certain to be acquitted by the Senate Republican majority in a trial that could be as short as two weeks.  

The articles of impeachment state that Trump tried to pressure Ukraine into interfering in the 2020 election to help him win, and then to thwart the investigation by blocking witnesses and denying documents to the House of Representatives.  

Central to the scandal is a July 25 telephone call in which Trump pushed Ukrainian President Volodymyr Zelensky to announce an investigation of Biden, his potential opponent in the November vote. Trump is accused of withholding nearly 400 million U.S. dollars in military aid for Ukraine's war against separatists, and refusing Zelensky a White House meeting, unless he opened a probe of Biden. 

On Sunday Trump's legal team issued a 110-page defense which claimed the House has accused him of no specific "crime," that their investigation was a "rigged process," and that Trump was within his rights to push Ukraine to investigate Biden.  

Jay Sekulow, one of Trump's lawyers, told the Senate Tuesday that the two articles of impeachment have only "a vague allegation about a non-crime allegation of abuse of power and obstruction of Congress."  

The impeachment process is deeply divisive among Americans – with polls showing the country split down the middle on whether the president should be removed from office, 10 months before voters go to the polls to decide whether to re-elect him.  

The president himself was in Davos, Switzerland for the World Economic Forum on Tuesday, where he repeated his longstanding characterization of impeachment as a "hoax."  

"We're meeting with world leaders, the most important people in the world and we're bringing back tremendous business," Trump said. "The other's just a hoax. It's the witch hunt that's been going on for years and frankly it's disgraceful."  

(With input from Reuters, AFP)

(Cover: U.S. Senate Majority Leader Mitch McConnell (R, front) walks to the Senate chamber at the Capitol in Washington, U.S., January 21, 2020. /AP Photo)