In Texas, Democrats were choosing between M.J. Hegar, an Air Force veteran who has the support of Senate Democrats, and State Senator Royce West in a runoff to determine who will take on Senator John Cornyn. Republicans were also deciding a number of nominees, including in an open seat in West Texas where Mr. Trump backed the former White House doctor, Ronny Jackson, in the primary.
In the race for the seat currently held by Representative Will Hurd, who is not seeking re-election, Mr. Trump and Senator Ted Cruz were on opposite sides of the runoff. The president offered a late endorsement of Tony Gonzales, the establishment favorite, while Mr. Cruz backed Raul Reyes, a more conservative candidate.
In terms of determining the balance of power in Washington, though, no race on Tuesday may have been more consequential than the Maine primary. The Senate race there is one of a handful that could determine control of the chamber, where Republicans have a majority, 53 to 47.
Ms. Gideon has already raised nearly $23 million, much of it from Democrats who are angry at Ms. Collins for confirming Justice Kavanaugh and not taking a harder line against Mr. Trump.
And now that Ms. Gideon is officially her party’s nominee, she will receive $3.7 million, which has effectively been sitting in escrow for the Democratic nominee since Ms. Collins’s Kavanaugh vote.
While she has been outraised in the first half of the year, Ms. Collins, who has raised over $16 million so far, has demonstrated an ability to keep closer pace with her opponent than some of her Republican colleagues. Both candidates will also be helped by multimillion dollar ad campaigns from party super PACs in a race that has already turned negative.
Early polls point to a competitive race in a state that has become politically bifurcated between a more conservative and rural north and a liberal-leaning and more densely populated south.