WASHINGTON — Special counsel Robert Mueller’s investigation into Russian contacts with President Donald Trump’s campaign has gained access to thousands of emails sent and received by Trump officials before the start of his administration, according to several people familiar with Trump’s transition organization. But the investigators did not directly request the records from Trump’s still-existing transition group, Trump for America, and instead obtained them from a separate federal agency that stored the material, according to those familiar with the Trump transition organization. A transition attorney sent letters Saturday to two congressional committees saying the General Services Administration had improperly provided the transition records to Mueller’s investigators.