Question: An election for the leadership of the Ulster Unionist Party (UUP) was held on 8 April 2017 at the party's Annual General Meeting, the 2017 contested election was triggered after incumbent Leader Mike Nesbitt, elected in 2012, announced following the 2017 assembly election his intention to step down as party leader, the 2017 election to the Northern Ireland Assembly was held on which date?

Context paragraphs:
John McCallister: John McCallister (born 20 February 1972) is a Northern Irish Unionist politician.  In 2007, was elected to the Northern Ireland Assembly as an Ulster Unionist Party (UUP) member for South Down.  On 14 February 2013, McCallister announced that he had resigned from the UUP due to its decision to engage in an electoral pact with the Democratic Unionist Party.  He was a co-founder of the NI21 party with fellow ex-UUP member Basil McCrea but resigned the following year following disputes with McCrea.  He re-contested his seat as an Independent at the 2016 election but lost his seat, receiving just 2.8% of the vote.

Trevor Clarke: Trevor Clarke MLA (born 28 July 1967) is a Democratic Unionist Party politician in Northern Ireland.  He was first elected in 2007 to the Northern Ireland Assembly as a Democratic Unionist Party (DUP) member for South Antrim.  Clarke lost his seat at the 2017 Assembly election, but was later co-opted by the DUP after Paul Girvan was elected in the 2017 general election.

Danny Kennedy: Danny Kennedy (born 6 July 1959) is an Ulster Unionist Party (UUP) politician and former MLA in Northern Ireland.  He was formerly deputy leader of the Ulster Unionist Party (UUP) Assembly Group and is a former Minister for Regional Development.  On 12 May 2016, Danny Kennedy was elected as Deputy Speaker of The Northern Ireland Assembly.  It was confirmed that he had lost his seat as an MLA for Newry and Armagh on 3 March 2017.

Ulster Unionist Party leadership election, 2012: The election for the leadership of the Ulster Unionist Party (UUP) was held on 31 March 2012.  The UUP holds an election for the office of Leader each year at its Annual General Meeting, which is normally returns the incumbent unopposed.  The contested election was triggered after incumbent Leader Tom Elliott, elected in 2010, unexpectedly announced on 8 March 2012 that he would not be seeking re-election.  Nominations closed on 16 March 2012.

Vanguard Unionist Progressive Party: The Vanguard Unionist Progressive Party (VUPP), informally known as Ulster Vanguard, was a unionist political party which existed in Northern Ireland between 1972 and 1978.  Led by William Craig, the party emerged from a split in the Ulster Unionist Party (UUP) and was closely affiliated with several loyalist paramilitary groups.  The presence of features such as an honour guard and a common salute led opponents to accuse it of being fascist.  The party was set up in opposition to power sharing with Irish nationalist parties.  It opposed the Sunningdale Agreement and was involved in extra-parliamentary activity against the agreement.  However, in 1975, during discussions on the constitutional status of Northern Ireland in the constitutional convention, William Craig suggested the possibility of voluntary power sharing with the nationalist Social Democratic and Labour Party.  In consequence the party split, with dissenters forming the United Ulster Unionist Party.  Thereafter Vanguard declined and following poor results in the 1977 local government elections, Craig merged the remainder of Vanguard into the UUP in February 1978.

Northern Ireland Assembly election, 2017: The 2017 election to the Northern Ireland Assembly was held on 2 March 2017.  The election was held to elect members (MLAs) following the resignation of deputy First Minister Martin McGuinness in protest over the Renewable Heat Incentive scandal.  McGuinness' position was not filled, and thus by law his resignation triggered an election.  It was the sixth election since the Assembly was re-established in 1998, and the first to implement a reduction in size to 90 MLAs (versus the previous 108).

Northern Ireland Assembly election, 2007: The third elections to the Northern Ireland Assembly were held on 7 March 2007 when 108 members were elected.  The election saw endorsement of the St Andrews Agreement and the two largest parties, the Democratic Unionist Party (DUP) and Sinn Féin, along with the Alliance Party, increase their support, with falls in support for the Ulster Unionist Party (UUP) and the Social Democratic and Labour Party (SDLP).

Ulster Unionist Party leadership election, 2000: The 2000 Ulster Unionist Party leadership election was triggered by the decision of Martin Smyth to challenge incumbent David Trimble over the party's direction in the implementation of the Belfast Agreement at the party's annual general meeting on 25 March 2000.  The UUP has held a leadership election every March since at least the Ulster Unionist Council constitution was altered in 1973, however it is rarely contested.  This is one of the few occasions when it has been contested.

Ulster Unionist Party leadership election, 2004: The 2004 Ulster Unionist Party leadership election was triggered by the decision of a group of UUP members to challenge incumbent leader David Trimble over the party's direction following the 2003 Northern Ireland Assembly elections at the party's annual general meeting on 27 March 2004.  The UUP has held a leadership election every March since at least the Ulster Unionist Council constitution was altered in 1973, however it is rarely contested.  This is one of the few occasions when it has been contested.

Ulster Unionist Party leadership election, 2017: An election for the leadership of the Ulster Unionist Party (UUP) was held on 8 April 2017 at the party's Annual General Meeting.  Elections are held each year, with the incumbent usually reelected unopposed.  The 2017 contested election was triggered after incumbent Leader Mike Nesbitt, elected in 2012, announced following the 2017 assembly election his intention to step down as party leader.  While initially, Robin Swann and Steve Aiken were expected to run against each other (with candidacies by Doug Beattie, Robbie Butler and Roy Beggs, Jr. also considered possible), in the end only Swann ran and was elected unopposed.

Supporting paragraphs: Ulster Unionist Party leadership election, 2017 Northern Ireland Assembly election, 2017
Answer: 2 March 2017