A federal appeals court is weighing whether special counsel Robert Mueller's appointment to lead the Russia investigation was constitutional.
At issue Thursday was whether Deputy Attorney General Rod Rosenstein had the authority to appoint Mueller.
The special counsel's office says yes. But lawyers for a former aide to longtime Trump confidant Roger Stone say no. The aide, Andrew Miller, brought the case because he doesn't want to testify before a grand jury as part of Mueller's investigation into whether Donald Trump's Republican campaign coordinated with Russia in 2016.
Mueller is focusing on Stone's connection to WikiLeaks. American intelligence agencies have concluded that Russian agents were the source of damaging information on Democrat Hillary Clinton that WikiLeaks released during her 2016 presidential campaign against Trump.
Stone has denied any wrongdoing.