Twitter announced the end of their free login service, unless we pay, and we are not going to pay. If you log into GovTrack using your Twitter account, make sure you don’t lose access to your GovTrack account. Log in and check that your profile has your current email address. https://www.govtrack.us/accounts/login
Then log out and use the 'Forgot your password?' link to add a password to your account. After that, you can log in with your email address and password.