WASHINGTON (Reuters) - Republicans have more reason to be nervous about the prospects of keeping control of the U.S. Congress this year after Democrats came out in force in Texas congressional primary elections.

Political campaign signs stand outside a polling station in Austin, Texas, United States March 5, 2018 ahead of the first statewide U.S. primary, which will be held in Texas. REUTERS/Jon Herskovitz

State figures show that more than 1 million Democrats cast votes in primary races across the state on Tuesday, almost twice as many as in 2014, the last time primaries were held for a midterm election.

Texas has long been a conservative bastion, but the much stronger turnout in the primary races to select nominees from their own party shows Democratic voters are highly motivated, threatening Republican control of the U.S. Senate and House of Representatives in midterm elections in November.

The surge in Democratic enthusiasm continued a pattern seen in earlier special elections and in the governor’s race in Virginia last year, with voters largely galvanized by their opposition to Republican President Donald Trump.

“Any increase in a primary electorate is some kind of a new voter, and that is a new level of engagement,” said Ed Espinoza, executive director of Progress Texas, a progressive strategy firm in Texas. “There’s a sense of populism. People want their democracy back.”

About 1.5 million Republicans voted in the primary races on Tuesday, only slightly more than four years ago.

Many Republicans watched the Texas returns with growing unease, but some said that with the general election still seven months away it was too early to suggest Democrats have an upper hand in taking either chamber of Congress.

“They still have a long way to go,” said Matt Mackowiak, a Republican consultant in Austin, Texas, who contended that without Trump on the ballot in November, Democrats may yet have problems motivating voters to come out to the polls.

Democrats need a net gain of two seats in the Senate and 24 seats in the House to gain control of those chambers.

While Trump won Texas handily in the 2016 presidential election, Democrats have targeted three House districts in suburban Dallas and Houston and in southern-central Texas, where Trump’s opponent, Democrat Hillary Clinton, won the majority of votes.

Tuesday’s turnout gave that effort a boost, although analysts say Republican incumbents remain favored to win those seats.

Opinion polls show that Trump is struggling with college-educated, affluent voters who live in cities such as Dallas and Houston.

“Some of the Trump effect is beginning to manifest itself,” said Joe Brettell, a Republican strategist in Houston. He said Trump’s hard-right positions on issues such as immigration and gun control were alienating moderate suburban voters that his party needs to remain competitive.

David Wasserman, a congressional elections expert in Washington, said that even in a primary election, the enthusiasm level showed by Democrats is consequential.

“That matters when it comes to knocking on doors, making phone calls, putting up signs - all of the grassroots activity that comes to winning congressional races in the fall,” he said.