Bull case for TLT 1) recession . Normally flight to safety so TLT will rise 2) cut in fed fund rates. TLT has long duration so more sensitive to rate changes  so TLT will rise more than short term treasury bills or notes 3) TLT has fallen more than 50%  Bear case for TLT 1) treasury debt situation. If US Gov can't solve their debt spiral , people will lose faith and not buy treasuries and this will affect TLT. However , the Fed can support by being the last buyer of treasuries , so there is a support .