(CNN) Once again, Democrats exceeded expectations in two special congressional elections. In the parlance of sports betting, their candidates "beat the point spread," the margin by which a favored team is expected to win. But what works in Vegas doesn't count for much in elections, where winning is the game.

In the four special elections to fill seats in the House of Representatives vacated by Republican incumbents to join President Donald Trump's Cabinet, the GOP has posted a 4-0 record. At the same time, the unsuccessful Democratic candidates in these special elections have vastly outperformed the party's nominees who ran in these same districts just eight months ago. And in the case of Tuesday's special elections in Georgia's 6th Congressional District and South Carolina's 5th Congressional District, the Democrats turned 20-point-plus blowout losses in 2016 into narrow four-point and three-point defeats, respectively.

But beating the spread hasn't gotten Democrats any new seats in Congress.

Georgia

In Georgia, Republican nominee Karen Handel beat back a challenge from Democratic hopeful Jon Ossoff, 52%-48%, in a suburban district north of Atlanta that was supposed to be ripe for an upset, because it was the kind of college educated, largely upper-income turf where Hillary Clinton had performed well against Trump. Indeed, it had the highest share of voters with at least a four-year college degree of any Republican-held House district in the country. In the 2016 presidential election, Trump narrowly beat Clinton 48%-47%. In 2012, GOP nominee Mitt Romney swamped Barack Obama in this district by 61%-37%.

The night did not start off well for Ossoff. When the first returns based on early absentee votes from the north Fulton County portion of the district were posted, Handel held a 51%-49% advantage. That was an ominous sign because in the first-round primary back on April 18, Ossoff had dominated the early absentee tally with more than 60% of that vote. This was an indicator that Republican voters in the district were more focused and mobilized than they were in the primary when they had 11 candidates to choose from.

Ossoff defeated Handel by roughly 58%-42% in the DeKalb County portion of the district where there are more African-American voters, but it made up less than a fourth of the overall electorate in the district. Handel bested Ossoff in the Cobb County section, a GOP stronghold, which contained just over 30% of the voters, by the same 58-42% margin. The battle came down to the Fulton County portion of the district, where almost half of the electorate resided. And when votes from the whiter, upscale neighborhoods Milton, Alpharetta and Roswell came in, Handel secured her victory, carrying Fulton by almost 53%-47%. Overall, roughly 260,000 were cast in this race, dwarfing the 210,000 who voted in the 2014 midterm election.

South Carolina

Republican candidate for Congress, Ralph Norman speaks with workers at a polling place in South Carolina's 5th Congressional District on Tuesday.

The big surprise of the night was how close Democrat Archie Parnell came to upsetting Republican Ralph Norman in the South Carolina CD 5 special election.

Norman managed to eek out a 51%-49% victory in a contest where there was surprisingly low turnout of about 88,000. In the 2014 midterm, almost 170,000 votes were cast.

Parnell won the southern portion of the district 57%-42%, which includes Fairfield, Lee and Sumter Counties with relatively high numbers of African-American voters. Norman won the smaller northwestern part of the district, 59%-40%, which includes Cherokee County next to the GOP stronghold of Spartanburg. But in York and Lancaster Counties, which include suburbs and exurbs of Charlotte, North Carolina, where more than half of the vote in the special election was cast, Norman, won 55%-44%.

Had the Democratic Party focused more attention and resources on the South Carolina special election, which was largely overshadowed by the contest in Georgia, it may have been able to pull off an upset. In the 2016 presidential race, according to party's own voter files, some 80,000 African-American voters in the district went to the polls. While not every one of them cast votes for Barack Obama, the vast majority surely did and they would have been disposed to backing the Democrat Parnell. In a race that was decided by less than 3,000 votes, an effective effort to mobilize the black vote in the district could have paid huge dividends.

Lessons for 2018

If Democrats are going to retake the House in the 2018 midterms -- which is certainly possible given the over-performance of their candidates in this year's special elections -- they're going to have to extend their focus beyond the borders of high-educated suburban districts held by Republicans where Clinton fared well in the 2016 presidential election. While the Georgia race was a tempting target after Trump turned in a relatively weak showing there in 2016, it still leaned Republican and Romney had won the district by a whopping 24 percentage points in 2012. In 2016, Trump won South Carolina's 5th Congressional District by 19 points, but Romney won it by just 12 points and it had an African-American population more than twice as large as the Georgia congressional district.

Another lesson from this year's House races is the importance of the party's "bench," the pool of potential candidates you can recruit from. While Democrats are bullish about many of their 2018 House prospects, in these four special elections, the Democratic bench was pretty thin compared to the lineup that Republicans fielded.

, the Democratic candidate was James Thompson, a civil rights attorney with no previous political experience who faced Republican State Treasurer Ron Estes. For the at-large Montana seat, the Democratic standard-bearer was country western musician Rob Quist, who was also making his political debut at age 69. His GOP opponent, Greg Gianforte, had also never held elected office, but he did run statewide in 2016 as the Republican nominee for governor, losing to incumbent Democrat Steve Bullock by less than four percentage points. In the Kansas 4th Congressional District race back in Aprilthe Democratic candidate was James Thompson, a civil rights attorney with no previous political experience who faced Republican State Treasurer Ron Estes. For the at-large Montana seat, the Democratic standard-bearer was country western musician Rob Quist, who was also making his political debut at age 69. His GOP opponent, Greg Gianforte, had also never held elected office, but he did run statewide in 2016 as the Republican nominee for governor, losing to incumbent Democrat Steve Bullock by less than four percentage points.

In Georgia, Democrat Ossoff was a 30-year-old former congressional aide going up against a veteran pol in Handel, who was a former secretary of state and former chair of the Fulton County Board of Commissioners. In South Carolina, Democrats turned to Parnell, a 66-year-old former managing director of Goldman-Sachs and ex-tax attorney for ExxonMobil, who also worked on the House Ways and Means Committee from 1976-1980. Republicans had as their standard-bearer Norman, a former five-term state legislator who had represented a chunk of vote-rich York County.

All told, Democrats had four political rookies on their team in these special elections, while Republicans had three candidates with significant experience in elected office and one who had narrowly lost a governor's race. That's an indication of how weakened the Democratic Party has become in the last decade at the state and local level, especially in red states.