All that talk of a Democratic blue wave sweeping congressional races in California could be for naught if a new poll is on target: It shows President Trump’s approval rating surging to 50 percent in Orange County, site of four tight races that could determine whether Republicans hold the House.

A more popular Trump is bad news for Democrats, who are trying to grab seven GOP-held congressional districts statewide that Hillary Clinton won in 2016, including the four in Orange County. That would give Democrats a big jump on their goal of flipping 23 seats nationally to regain the House.

Democrats are banking on the president’s unpopularity to help them win those seats. In April, the nonpartisan Berkeley IGS Poll indicated that Trump had just 38 percent support in Orange County. A March poll from the nonpartisan Public Policy Institute of California indicated that a mere 36 percent of all adults in Orange and San Diego counties approved of the president.

Two months ago, Republican pollster John Thomas did a survey in Orange County that found Trump’s approval rating at 43 percent. But last week, his poll of 450 likely voters in the county showed that 50 percent of respondents viewed the president favorably. The margin of error was plus or minus three percentage points.

One reason for the Trump uptick in the O.C. is that the number of voters who believe the country is on the right track has grown 10 percentage points over the past two months, Thomas said. He is advising Orange County Supervisor Shawn Nelson, who is running for the House seat held by soon-to-be retiring Rep. Ed Royce, R-Fullerton.

“If that holds and the trend line continues, ” Thomas said, “then it’s buh-bye blue wave.”

Other surveys have found high approval for Trump’s handling of the economy, which historically is a good indicator of overall satisfaction with a president’s performance. A CBS News poll released Sunday showed that 68 percent of the adults surveyed thought Trump’s policies “were responsible for the current state of the economy.”

But organizers for NextGen America, a progressive organization funded by billionaire former hedge fund manager Tom Steyer, believe a Democratic sweep in November is still possible. The group is spending $350,000 to try to turn out 200,000 voters ages 18 to 35 in the four targeted Orange County districts.

NextGen America is focusing on turning out people who typically don’t vote in midterm elections. Statewide, only 3.7 percent of voters between ages 18 and 25 voted in the 2014 California primary, according to a UC Davis study.

“There’s nowhere to go but up,” said Ben Wessel, NextGen’s deputy political director.

While Thomas’ poll may have shown Trump’s popularity rising among likely voters, Wessel said, “we don’t spend a lot of time talking to likely voters. And among the people we’re talking to, I can tell you anecdotally that his approval rating is more like 5 percent.”

— Joe Garofoli

Speaking of the O.C.: In another sign that California’s “blue wave” may be in danger of ebbing to a trickle, a leading political prognosticator is suggesting that Republicans are on the rise in the contest for a couple of open congressional seats.

In both Orange County’s 39th District and 49th District, which straddles the border between Orange and San Diego counties, the Cook Political Report has moved the races from “lean Democrat” to “toss-up.”

The report, which describes itself as “an independent, nonpartisan newsletter that analyzes elections and campaigns,” said a strong economy and the possibility of improving relations with North Korea have boosted President Trump’s popularity across the country. That’s especially true in Orange County, where a GOP pollster has the president’s favorability rating at a new high of 50 percent.

That’s way better than it was last year, when veteran GOP Reps. Ed Royce of Fullerton and Darrell Issa of Vista (San Diego County) took a look at the changing demographics of their districts — and Californians’ anger at Trump — and decided they would rather retire than face a grindingly tough re-election race.

Adding to that relatively upbeat news for Republicans is California’s top-two primary, where the leading two vote-getters, regardless of party, advance to the Nov. 6 election. And while Orange and San Diego counties aren’t the GOP bastions they once were, there still are plenty of conservative voters there who will vote for a Republican — any Republican — before they’d consider a Democrat.

In recent weeks, both state and national Democratic groups have been working to both bash the GOP hopefuls in those districts and to smooth over the rifts between their own contentious candidates.

The good news for California Democrats is that a toss-up race is just that, one where they’re seen as having at least an even chance of flipping those districts and three other Republican-held seats in the state that Cook puts in that same category. Winning as many of those districts as possible is key to the party’s hopes of flipping 23 GOP-held seats nationwide and winning back the House.

“It’s also important to remember that voter intensity matters just as much as president approval ... and Republicans still can’t point to hard election data that proves their base has suddenly closed the ‘intensity gap’ in the past few months,” the Cook report said.

— John Wildermuth