Five poll numbers that should make Democrats uneasy

All good points. One factor to consider is Independent leaners since the growth of Independents are a result of voters leaving both parties. Although the link below gives a lot of data on the perspectives of Independents, this one struck me as important:

Why do Republican leaners choose not to identify as Republicans? About half (52%) say a major reason they do not affiliate with the party is their frustration with its leaders; 40% say it is because they disagree with the party on important issues.

Among Democratic leaners, no single reason stands out. A third say a major reason they do not identify as Democrats is that they disagree with the party on key issues, while 28% cite frustration with the party’s leadership.​

Although Independents are split almost 50/50 right and left leaners, note that the reasons Republicans became Independents are more focused than those Democrats who became Independents. Just guessing, but if one group is more focused than another, they're more likely to vote as a block and, therefore, their behavior is more predictable. Since the Left-leaning Independents are scattered all over the map, it's much difficult to predict their behavior such as how they'd vote in an election. Just so we're clear, I'm not saying the Right-leaning Independents will vote Republican, just that they'll tend to vote the same way depending on the issue.

 

And a very corrupt and self-serving part.

 

Indeed, that is exactly what are the Alt Right - corrupt and self serving.

 

Probably so. I never really identified with either major party. But probably as an Eisenhower Republican since IKE was president when I grew up. Although my folks would have been classified as old yeller dog democrats. They would sooner vote for an old yeller dog than a republican. I'm frustrated with both parties leaders as they seem to put the good of their party over the good of the country.

The disagree on key issues by the Democrats, down south that would probably be gun control. Our local Democratic leaders are very pro-second amendment. Some religious and anti-abortion. One told me it is almost impossible to be one of faith and be a good Democrat anymore. He is thinking about becoming a Republican, but put it off because he doesn't like Trump. The south had a lot of pro-defense democrats which really aren't anymore. They all became Republicans or died. Just some of the issues that may have lead a Democrat to abandon the party down here.

I do think a lot of independents tend to vote their pocket book than issues which could explain the dynamic shift of overwhelming support for one party in one election to the other party in the next election. 2006 was the beginning of a recession along with Iraq and indies went 57% for the democrats. 2010, the recession was still in place but lessening, so indies went 57% for the Republicans. Although I place the main reason as to the ACA since they didn't want it and the Democrats in congress basically told them to stick it where the sun doesn't shine. They were angry.

I suppose there are many reasons why the two major parties are losing affiliation or membership. I think the more moderate of each party are the ones that left each party. Leaving the Democrats more extreme left and the GOP more extreme right. I think we see that in Washington today. Than in 2006 liberal progressive democrats defeated the more moderate Republicans in congress to gain control. Then in 2010 the very conservative republicans defeated mostly the moderate blue dog democrats leaving congress with extremes and no one in the middle to broker compromise or to talk across the aisle to work things out. Hardcore now reigns in Washington.