Washington: US Republican presidential contender Donald Trump called on Wednesday for the resignation of Supreme Court Justice Ruth Bader Ginsburg, describing her as mentally unfit after she lambasted him in a series of media interviews. In interviews this week, Ginsburg told CNN she viewed Trump as a "faker" and said she was worried about the country's future if he won the White House in November. Her comments have sparked a firestorm of criticism and have enraged Republicans. Republican House of Representatives Speaker Paul Ryan, in a CNN interview on Tuesday, called Ginsburg's comments "biased and out of the realm". Trump, who has called Ginsburg's comments inappropriate, stepped up his criticism on Wednesday in a Twitter post. Ginsburg, 83, had "embarrassed all by making very dumb political statements," he said, adding, "Her mind is shot - resign." Trump was not alone in the rebuke. In an editorial on Wednesday, the New York Times said that while there was no legal requirement for her to refrain from commenting on the presidential campaign, Ginsburg should uphold the court's tradition of silence in political campaigns and drop the "punditry and name-calling." The furore over Ginsburg's comments comes as Trump prepares for the Republicans' July 18-21 convention that will formally nominate him as the party's presidential candidate for the November 8 election. Trump, who needs to energise conservatives in his party who are divided over his unorthodox candidacy, has emphasised the importance of naming conservative justices to the Supreme Court. Ginsburg is among the liberals on the court, which has been ideologically split between four liberals and four conservatives since conservative Justice Antonin Scalia died in February. US Supreme Court justices are not required to follow the code of judicial conduct that applies to judges on lower federal courts. The code, set by the US Judicial Conference, says judges should not "make speeches for a political organisation or candidate, or publicly endorse or oppose a candidate for public office." Still, the judges on the country's top court typically try to stay out of the political fray. In public remarks earlier this year, Chief Justice John Roberts stressed it was important for the justices not to be seen as political players, saying criticisms of partisanship, which he described as inaccurate, were damaging to the court's reputation. "We don't work as Democrats or Republicans," he said. Ginsburg was not immediately available for comment on Trump's remarks and the Times editorial. The Supreme Court, whose nine justices are nominated by the US president to lifetime appointments, is in the spotlight this presidential election cycle after Scalia's death. The Republican-controlled US Senate has refused to take up Democratic President Barack Obama's nominee to replace Scalia, Merrick Garland. Republicans have said the next president should be allowed to nominate a replacement for Scalia. The next president, potentially serving two four-year terms, could have the opportunity to appoint up to three new justices, not including Scalia's replacement. Ginsburg is the oldest of the justices. Justice Anthony Kennedy turns 80 on July 23, while Justice Stephen Breyer turns 78 in August. US Senator Bernie Sanders of Vermont, who dropped his presidential bid on Tuesday and endorsed rival Hillary Clinton to be the Democratic candidate for the election, told ABC's "Good Morning America" he agreed with Ginsburg. "I think that Trump is a total opportunist," Sanders said. "I do not believe anything that comes out of his mouth."