(Updates with confirmation of National Economic Council staffer's resignation)
By Susan Heavey and Lisa Lambert
WASHINGTON, Feb 14 (Reuters) - President Donald Trump faced new pressure on Wednesday from his Republican allies in Congress over domestic abuse allegations against a former aide as lawmakers questioned whether his administration has properly vetted top staffers.
Republican Representative Trey Gowdy, chairman of the House Oversight Committee, said he was investigating when the White House learned of "potential derogatory or disqualifying information" about former Staff Secretary Rob Porter.
Porter left the White House last week after two former wives said he abused them. He has denied the accusations.
"The chronology is not favorable for the White House," Gowdy said on CNN.
Republican House Speaker Paul Ryan, meanwhile, said the White House should improve its vetting process.
"If a person committing domestic violence gets into government, then there's a breakdown in the system," Ryan said at a news conference.
Porter's departure has raised questions about how long top staffers like White House Chief of Staff John Kelly knew about the allegations and whether it was a security risk to have Porter working in the White House.
Some officials within the White House and some of the president's outside advisers have singled out Kelly for criticism for his handling of the episode.
One source said Trump has talked privately about replacing Kelly. A variety of names has been making the rounds as potential replacements, such as top White House economic adviser Gary Cohn, the source said.
Vice President Mike Pence told the Axios news media outlet that the White House could have handled the Porter case better but that he has great respect for Kelly.
"John Kelly has done a remarkable job as chief of staff for the president of the United States, and I look forward to continuing to work with him for many, many months to come," Pence said.
Trump was pressed by reporters on whether he opposed domestic abuse after offering glowing comments about Porter.
"I'm opposed to domestic violence and everybody here knows that," Trump said during an Oval Office event. "I'm totally opposed to domestic violence of any kind. Everyone knows that and it almost wouldn't even have to be said."
On Friday, White House speechwriter David Sorensen resigned after revelations that his former wife had accused him of domestic violence.
Another White House staffer, National Economic Council policy aide George David Banks, told Reuters he had quit after he was told on Tuesday that he had not cleared a security check due to past marijuana use. Politico first reported his resignation.
Porter had been operating under a temporary clearance that have him access to some sensitive information without a final clearance. The White House has not offered a definitive explanation of when top officials first got word of problems in Porter's background.
The White House has said that Kelly asked Porter to resign when he became "fully aware" of the accusations last Wednesday, the same day the Daily Mail published photos showing one of Porter's former wives with a black eye.
The White House was still working on Porter's security clearance at that point, according to White House spokeswoman Sarah Sanders.
But Federal Bureau of Investigation Director Christopher Wray has contradicted that version of events, telling Congress on Tuesday that the FBI had completed Porter's security clearance background check in July.
Porter had been rising in Trump's inner circle and had been talking to Kelly about a promotion before his departure, according to a source familiar with the situation.
Gowdy said on CNN he would also ask the FBI how it conducts background checks.
Roughly a dozen top White House officials, including Trump's son-in-law Jared Kushner, have yet to achieve a full security clearance, according to Kushner's lawyer, Abbe Lowell.
Kushner's extensive holdings and his travels have delayed the process, and there is no concern about either the vetting process or Kushner's ability to do his job, Lowell said.
Trump has repeatedly defended Porter without expressing sympathy toward domestic violence victims.
The scandals follow months of allegations by women about sexual harassment or abuse at the hands of powerful men in entertainment, business and politics.
More than a dozen women have accused Trump of making unwanted sexual advances against them in the years before he entered politics. Trump has denied the accusations and has accused Democrats and the news media of orchestrating a smear campaign. (Additional reporting by Valerie Volcovici; Writing by Andy Sullivan and Steve Holland; Editing by Jonathan Oatis and Cynthia Osterman)
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