Trump is the first US president who facing an impeachment trial after he left the presidency.
'We also urge you to take steps to control the activities of groups, such as the Rashtriya Swayamsevak Sangh,' said the letter signed by 34 top American lawmakers.
"We must also look beyond this terrible moment and decide what we as a nation are willing to do to prevent hatred, gun violence and domestic terrorism," said Congressman Ann Kirkpatrick from Arizona.