when can a president call a special session of congress
Special session This power exists for urgent or extraordinary situations that require congressional action when Congress is adjourned. Presidents have exercised this power 46 times to recall only the Senate and 28 times to recall both Chambers of Congress, most recently by Harry Truman in 1948.[2]
Lame-duck session The possibility of a lame-duck session of Congress in the modern sense began in 1935, when the 20th Amendment to the Constitution took effect. Under this amendment, ratified in 1933, Congress meets in a regular session on January 3 of each year, unless in the previous session it passes a law changing the date. Also, the terms of Members begin and end on January 3 of odd-numbered years. Under these arrangements, any meeting of Congress after election day (in November of even-numbered years), but before the following January 3, is a lame duck session.