President Donald Trump announces that the Republican Party will hold its first-ever midterm convention in Dallas this September to rally voters and shore up fragile House and Senate majorities.The Republican National Committee approved rule changes earlier this year to permit a midterm gathering that Mr. Trump presents as a showcase for the America First agenda and policy wins on tips, overtime taxation, border enforcement and energy production.Holding the event in Texas highlights the competitive Senate contest between Republican Ken Paxton and Democrat James Talarico; Mr. Paxton defeated John Cornyn in the primary and remains controversial because of an impeachment and a securities fraud case.Organizers say the two-day program at the American Airlines Center will be shorter and rally-like with appearances by entrepreneurs, first responders and job creators as Republicans aim to convert enthusiasm into turnout ahead of the November election.