(Reuters) - Highlights of the day for U.S. President Donald Trump’s administration on Tuesday: Trump endorses Republican legislation to replace the Obamacare healthcare law, but it faces a rebellion by conservative groups and lawmakers who denounce it, complicating its chances for congressional approval. The House Republican health insurance plan suggests post-Obamacare health insurance will be less affordable, investors, insurers and industry sources say, raising questions about future enrollment and insurance company participation. Large U.S. pharmaceutical and biotechnology company shares sell off after Trump says he is working on a system to reduce drug prices. Senate Democrats, seeking to capitalize on revelations about Trump campaign contacts with Russia, urge a top Republican lawmaker to obtain the president’s tax returns as a matter of national security. The lawyer who will take over an investigation into Russian meddling in the U.S. presidential election, if he wins Senate confirmation to become deputy attorney general, rebuffs Democrats’ demands for the appointment of a special prosecutor in the case. The Senate Armed Services Committee overwhelmingly approves Army Lieutenant General H.R. McMaster as Trump’s second national security adviser, despite concern about his handling of a sexual assault case. White House spokesman Sean Spicer says he has no reason to think Trump does not support FBI Director James Comey after a dispute over the president’s allegation without evidence that he was wiretapped last year. The chairman of the U.S. House of Representatives intelligence committee says he has seen no evidence to support Trump’s allegation he was wiretapped by then-President Barack Obama during the 2016 presidential campaign. The Trump administration pledges in a statement to show “great strictness” over restrictions on Iran’s nuclear activities imposed by a deal with major powers but gives little indication of what that might mean for the agreement. The United States starts deploying the first elements of its advanced anti-missile defense system in South Korea after North Korea’s test of four ballistic missiles, U.S. Pacific Command says, despite angry opposition from China. Senate Minority Leader Chuck Schumer and 11 other Democrats say it is critical that the Trump administration retain new vehicle fuel efficiency rules, arguing that the higher standards are achievable. Trump is to nominate Washington lawyer Noel Francisco for the position of solicitor general, the government’s top advocate before the U.S. Supreme Court, according to two sources familiar with the hiring process. 