The bill proposing a commemorative half dollar for the 150th Anniversary of James Cook's sighting of, and subsequent landing on, the present-day Hawaiian Islands (originally known to Europeans as the Sandwich Islands) in 1778 was introduced in the House of Representatives ("House") by Victor S. (Kaleoaloha) Houston of the Territory of Hawaii - a non-voting (Republican) delegate to the House of Representatives - in December 1927. It was passed in the House on February 20, 1928 without debate.
By late February 1928, Delegate Houston was so confident that the coin bill would pass in the House, that he sent word to Edgar Henriques, the Executive Secretary of the Captain Cook Sesquicentennial Commission ("Commission") the Friday before (February 17th) the bill was considered in the House. He recommended that the Commission proceed with its celebration plans under the assumption that the bill would pass. Good thing for him, he was correct! (I don't think Delegate Houston was channeling his innermost Nostradamus at the time, the outcome of many (but not all) bill votes are essentially "known" before the vote is actually taken.)
Note: Delegate Houston had also introduced a Joint Resolution that authorized the President to invite the government of Great Britain to participate in the anniversary celebration. This Resolution also passed the House on February 20, 1928. More about this Resolution can be found here: 1928 Hawaiian Discovery (European) Sesquicentennial - Invitation/FundingThe bill was considered and passed in the Senate on March 2, 1928, and was signed into law by US President Calvin Coolidge on March 7, 1928. (The same day as the Joint Resolution.)
1928 Hawaiian Discovery (European) Sesquicentennial Half Dollar

For more of my topics on commemorative coins and medals, including more stories about the Hawaiian half dollar, see:
Commems Collection.