candidates supported by both major parties
As early as the first Federal elections in 1788, there were candidates, who while alligned with one party or another, was supported in the press by both parties in a particular election.
Convention: An assembly of delegates or representatives for some special or occasional purpose.
Oxford English Dictionary
Several states had movements for Constitution Conventions during the years 1787 – 1825 and in most of them popular elections were held for choosing Delegates. Not all of these endeavors for convening Conventions were successful. Those that were successful however, often made substantial changes to state governments.
1801 - 1823: Massachusetts, New York, Pennsylvania
Office Scope: State / District
Role Scope: District / County / Ward