*Editor's note: This story has been updated throughout.

Presumptive Republican presidential nominee Donald Trump leads Democratic rival Hillary Clinton by 8 percentage points in Texas, according to a University of Texas/Texas Politics Project Poll released Monday.

Trump is ahead of Clinton 41 percent to 33 percent in a head-to-head matchup, the poll found. Nineteen percent indicated support for "someone else," and 8 percent said they "haven't thought about it enough to have an opinion."

Trump's advantage over Clinton narrows to 7 percentage points when Libertarian Party nominee Gary Johnson was added to the choices. He garners 7 percent support, leaving Trump with 39 percent and Clinton with 32 percent.

The previous two Republican nominees easily won Texas by double digits — John McCain by 12 in 2008 and Mitt Romney by 16 in 2012.

Asked about their reasoning, 55 percent of the Trump supporters said they don't want Clinton to become president, while 45 percent said they made their choice because they want Trump in the White House. Among Clinton supporters, 57 percent said they want her to be elected, while 43 explained their choice as a vote against Trump.

The two candidates remain very unpopular: 56 percent of the poll respondents have an unfavorable opinion of Trump, and 59 percent have an unfavorable impression of Clinton. They aren't crazy about the political parties, either: 50 percent have an unfavorable opinion of the Democratic Party, and 51 percent have an unfavorable view of the Republican Party.

The University of Texas/Texas Politics Project Poll echoes a survey that was commissioned by Texas Democrats and released Wednesday. It found Trump leading Clinton by 7 percentage points in Texas, 37 percent to 30 percent.

The University of Texas/Texas Politics Project Poll of 1,200 registered voters was conducted June 10-20 and has an overall margin of error of 2.83 percentage points.

Disclosure: The University of Texas at Austin has been a financial supporter of The Texas Tribune. A complete list of Tribune donors and sponsors can be viewed here.