The event comes fewer than 70 days before the midterm election and as Paxton trails Talarico in recent polling. The New York Times reported that entry to Thursday's fundraiser began at $10,000 per couple, with some donors paying more than $400,000 per couple.
Trump said he planned to play an active role in Paxton's campaign.
"I'm going to help Ken Paxton, and I'm going to spend a lot of time in Texas," Trump said.
A new poll from the non-partisan "Texas Public Opinion Research" has Talarico with his biggest lead yet, leading Paxton by six percentage points. Amongst independents, the poll has Talarico leading by 21 points.
"These polls that keep coming out that show Talarico ahead, even if it's just by a little bit, encourage his supporters, encourage other people to say, well, hey, maybe we can do it this time," said Democratic political consultant Sue Davis.
Amongst Hispanic voters, the poll has Talarico leading by 17 percentage points, and amongst black voters, 65 percentage points. Paxton leads with white voters by 14 percentage points.
Gov. Greg Abbott downplayed the August polling during an appearance on ABC's 'This Week', arguing that the final result will be determined at the ballot box in November.
"What matters in elections is not in August; what matters in elections is November," Abbott said.
Carroll Robinson, a Texas Southern University political science professor, said the stakes extend beyond Texas. Republicans, he said, must protect Texas if they hope to preserve their Senate majority.
"To save the Senate, they absolutely have to try to hold on to Texas," Robinson said.
If Talarico were to win in November, he would become the first Texas Democrat elected to the U.S. Senate since 1988.
Trump is scheduled to remain in Houston on Friday for an appearance at Johnson Space Center, where he will award the Congressional Space Medal of Honor to the three American astronauts on the Artemis II mission.