Connecticut allows fusion, and the Working Families Party and the Independent Party have put fusion to good use in that state. In 2016 both parties made significant gains in voter support.
The Connecticut Working Families Party polled 5.51% for U.S. Senate. It had nominated the Democratic nominee, Richard Blumenthal, and Blumenthal received 87,948 votes under the WFP label. This election was the first time the WFP had polled over 5% of the vote in a statewide election in any state (not counting races in which the Republican Party didn’t run anyone, which occurred for Massachusetts Auditor in 2006 and Oregon Attorney General in 2008).
The WFP also polled 5.81% of the Connecticut vote for U.S. House (in the four districts in which it had a nominee), its best statewide showing ever for that office. In those four districts it had nominated the Democratic nominee. In one district it had no nominee.
The Independent Party, which almost entirely nominates persons who are also Republican nominees, didn’t have any statewide nominees in 2016. But for State House, it appeared on the ballot in a majority of the districts, something no other party, other than the Democratic and Republican Parties, has done in Connecticut in at least 100 years. Even the Socialist Party, which elected legislators in Connecticut in the 1930’s, did not have nominees in a majority of House districts during that decade. As a result of having so many nominees, the Independent Party got more cumulative votes for each house of the legislature than the Working Families Party did. The Independent Party got 3.87% of the State Senate vote in the districts it contested, and 4.64% of the House vote in the districts it contested.
The Working Families Party has been running for legislature in Connecticut starting in 2002, and for congress since 2004. The Independent Party has done so starting in 2008. Both parties nominate by convention, not primary. In October 2016, the Independent Party had 21,216 registered members and the Working Families Party had 323 registrants. The WFP does not encourage its supporters to register into the WFP; the WFP prefers that they register as Democrats so that they can vote for WFP-prefered Democrats in the Democratic primary.