Democrats' victory parade looks like it will hit a wall in Arizona

Later this month, however, the Democratic victory parade looks more likely than not to hit a wall in Arizona.

Republican Debbie Lesko is a strong favorite over Democrat Hiral Tipirneni in the race to replace Republican Trent Franks in Arizona's 8th congressional district. The only poll to come out publicly is an internal one from Tipirneni, which had Lesko up double digits. CNN's own analysis and nonpartisan handicappers from places like the Cook Political Report and Inside Elections have Lesko heavily favored.

If Lesko's win comes to fruition, it's a demonstration that even in bad environments, a potential wave doesn't hit equally in all places.

Arizona's 8th is quite friendly to Republicans. Trump carried it by a little more than 20 percentage points. That's similar to how Trump did in Pennsylvania's 18th district. A key difference, however, is that the Arizona district doesn't have the same Democratic tradition that the Pennsylvania one does. Republicans hold a voter registration advantage of nearly 80,000 in Arizona's 8th, while there are more registered Democrats than Republicans in Pennsylvania's 18th. To put it in some historical context, Arizona's 8th is a place where Ronald Reagan won easily in 1984 compared to Walter Mondale winning in Pennsylvania's 18th.

The Arizona district is also a place where the Republican Party's lack of enthusiasm is muted by voting laws. Early voting and no excuse absentee voting in the law of the land in Arizona. That means Republican voters who might be disenchanted don't have to crawl across hot coals to cast a ballot. That's a very different situation from Pennsylvania where there is no early voting and you need an excuse to cast an absentee ballot.

But perhaps the biggest difference between the two races is the quality of the candidates. There are no reports that Tipirneni is a bad candidate by any stretch, but Lamb was an excellent candidate by almost everybody's judgment. Meanwhile, Republicans caught a break when Lesko was nominated instead of Steve Montenegro, who was involved in a texting scandal. In Pennsylvania, Republican Rick Saccone was regarded as a lackluster candidate.

Now, we don't know what the actual outcome in Arizona is going to be. It seems quite conceivable that Tipirneni is going to improve (and potentially significantly) on Democrat Hillary Clinton's showing in the district. That, in and of itself, is a good sign for Democrats because what's most important in understanding what special elections mean for the national political environment is how the results compare to the partisan baseline. Most districts Democrats will target in the fall will be far less Republican leaning than Arizona's 8th. A 10-point swing towards the Democrats won't make them a winner in this district, but it will in many swing districts.

Even if Lesko ends up doing about as well as Trump does, it's not necessarily a sign that Republicans are all of a sudden on the mend. To fully comprehend what special elections mean for the national political environment, it's best to look at a lot of different elections. Any one election result can mislead you. This year Democrats have been outperforming the partisan baseline in special elections by double-digits.

Think about the last two times the House switched hands: 2006 and 2010. There were special elections right around this time of year where the majority party candidate won, which sent off a false signal of security.

In 2006, Republican Brian Bilbray held back Democrat Francine Busby in California's 50th district. The race was closely watched for what it meant for the fall. The result was seen as a "glimmer of hope" for Republicans, as Slate's John Dickerson wrote. It shouldn't have been. Democrats would have a net gain of 30 seats and take the House later that year.

In 2010, Democrat Mark Critz defeated Republican Tim Burns in Pennsylvania's 12th district. Critz won even though Republican John McCain had actually won the district in 2008. CBS News' Marc Ambinder said in reference to the result that "pundits in Washington are going to have to revise our thinking about whether this is a wave election year for Republicans." No thinking actually needed to be revised. Republicans would net a gain of 63 seats in the fall and take control of the House.

In both the Bilbray and Critz instances, the races were significantly different than the average swing other special elections were showing that year. The averages were signaling that the majority party was in major trouble, and the averages ended up being correct.

Already in this cycle, we've seen Democrats fall short in the much-hyped Georgia 6th district special election. Democrat Jon Ossoff actually lost the district by a slightly wider margin than Clinton did in 2016. The average swing though continued to be heavily in the Democrats' direction and they went on to flip a Senate seat in Alabama and a House seat in Pennsylvania.

Indeed, that's a signal of what's probably going to happen in the fall. Democrats, on average, are probably going to do better in most districts than they did in 2016. In a number of them, however, they are going to do worse. The national political environment is key, but candidates and campaigns still do matter.