The highest turnout in Nassau and Suffolk counties since at least 2002 in a midterm election ushered in major Democratic victories in Nassau County and helped the party take over the State Senate.
But Republican bastions in Nassau as well as strength in Suffolk helped GOP congressional members hold on, according to a Newsday analysis of election results.
Turnout topped 53 percent in Suffolk and 51 percent in Nassau, not counting thousands of absentee paper ballots still to be processed, according to the counties' boards of election.
That compares with voter turnout of 36 percent in Suffolk in 2014; 45 percent in 2010; 43 percent in 2006; and 44 percent in 2002, according to the Suffolk County Board of Elections.
In Nassau, turnout was 35 percent in 2014; 43 percent in 2010; 44 percent in 2006; and 44 percent in 2002.
Political leaders and analysts attributed the surge to Democrats who wanted to signal their opposition to President Donald Trump and independent voters unhappy with the performance of Republicans in Washington, D.C.
"The blue wave on Long Island was driven particularly by Trump, particularly in areas where he's underwater," said Lawrence Levy, executive director of Hofstra University's National Center for Suburban Studies.
High Democratic turnout also was a "testament to the local Democratic Party," where candidate "profiles, personal histories and positions on policies were in sync with local communities."
Nassau Republican chairman Joseph Cairo called the night "disappointing."
Three of four State Senate seats that flipped to Democrats are in Nassau County.
He said Republicans' message about the Senate — that the GOP would be a watchdog for Long Island's interests in otherwise Democrat-controlled Albany — "didn't register with voters the way we thought it would."
Dissatisfaction with Trump in some areas "was certainly a factor," Cairo said.
"Younger people in particular were animated by the harshness of the president," Cairo said.
However, he credited Trump with energizing Republicans in some areas of Nassau, helping to stave off what could have been bigger losses for the party.
Cairo pointed to the victory of Rep. Peter King (R-Seaford) over Democrat Liuba Grechen Shirley in the 2nd Congressional District. The district contains parts of Suffolk and Nassau counties, but King's entire margin of victory came from Nassau, unofficial results show.
Cairo also pointed to Republican Mike LiPetri's victory over freshman Democratic Assemb. Christine Pellegrino in the 13th District. Pellegrino won the seat in the heavily Republican district in a 2017 special election.
Nassau Democratic chairman Jay Jacobs said the Democratic vote in Nassau was particularly strong in some areas with large numbers of minority residents, including Freeport, Hempstead, Roosevelt and Baldwin. In some of those communities Democratic turnout was 140 percent higher than in 2014, Jacobs said.
Democrats and independent voters "were unhappy with Donald Trump — the nastiness, the tone coming out of Washington," Jacobs said.
Jacobs said King's success in Nassau came in Republican strongholds. "A Democrat winning in Massapequa is like finding a penguin in the desert. It's just not meant to be," Jacobs said.
Democrats' didn't do as well in Suffolk overall as in Nassau, leaders of both parties said.
While Nassau County backed Gov. Andrew M. Cuomo by 55 percent to 41 percent over Republican Marc Molinaro, for example, Suffolk's vote favored Cuomo 50 percent to 46 percent in Tuesday's election, according to Suffolk and Nassau boards of elections.
"We stemmed the tide pretty well in Suffolk," said Suffolk County Republican chairman John J. LaValle. But "it was a difficult day across New York" for Republicans, he said.
In the 1st Congressional District in eastern Suffolk, Rep. Lee Zeldin (R-Shirley) beat Democratic challenger Perry Gershon 52 percent to 46 percent, unofficial returns show.
However, Suffolk County Legis. Monica Martinez (D-Brentwood) beat GOP Assemb. Dean Murray for the vacant State Senate seat of departing Sen. Tom Croci.
Michael Dawidziak, a political consultant who works primarily with Republicans, said turnout in minority areas of Brentwood and Central Islip helped Martinez.
Suffolk Democratic chairman Rich Schaffer said, "I think that suburban women in particular reacted negatively to the harsh Republican agenda. They came back to our party this year." Also, voters who had not participated in the past showed up this year, he said.
Yet Schaffer said polling shows Trump remains popular in Suffolk, with an approval of around 50 percent.
"Suffolk County is a pretty moderate to conservative county. Democrats can win when we present ourselves to the public as moderate, fiscally conservative, socially conscious people," he said.
But Republican Suffolk Board of Elections Commissioner Nick LaLota noted that in the countywide race for county comptroller, GOP incumbent John M. Kennedy Jr. was leading Democrat Jay Schneiderman by 8,623 votes, with more than 26,000 absentee ballots to be counted.
"With Republicans winning tight races for Congress, Democrats doing the same in the State Senate, and with the comptroller race coming down to absentees, it’s clear Suffolk County is more purple than blue or red," LaLota said.