President Donald Trump would agree to an interview with Special Counsel Robert Mueller’s investigators if it’s limited to questions on whether his presidential campaign colluded with Russia in the 2016 election, lawyer Rudy Giuliani said on Monday night.

Trump is demanding in return that he isn’t asked questions about obstruction of justice in the probe into election interference, under a proposal the president’s legal team submitted to Mueller, Giuliani said.

The president’s legal team is concerned that Mueller and his staff might believe witnesses who contradicted Trump’s account, such as former FBI Director James Comey, Giuliani said. That could leave the president vulnerable to a perjury charge, he added.