Why go on a roller coaster?  It’s not the destination, it’s the ride — right?  Keep that in mind as we plumb the ever-entertaining and decreasingly informative Gallup generic Congressional survey.  This week starts with an odd-numbered day, which means Republicans must be leading again.  Voila!

Forty-eight percent of registered voters favor Republican congressional candidates and 43% favor Democratic candidates in Gallup’s national generic ballot for the week of Sept. 6-12.

Registered-voter preferences for Congress since the beginning of August have averaged 48% for Republican candidates and 43% for Democratic candidates, identical to this week’s results. While there have been a few instances in recent months when the Republicans were not ahead to at least some degree — including in mid-July, when the Democrats were up by six percentage points, and last week, when the parties were tied at 46% — the broad picture has generally been positive for the Republicans.

Currently, 90% of Democratic voters plan to vote for the Democratic congressional candidate in their district, while 96% of Republicans favor the Republican, matching the highest level of Republican loyalty Gallup has found all year. Independents continue to favor Republican over Democratic candidates, now by a 10-point margin, 44% to 34%.

Why is this decreasingly informative?  First, Gallup has been unreliable even within its own trending.  Republicans lead by six, then Democrats lead by five, and then Republicans go back up by six, and then it’s suddenly even.  Six Flags doesn’t provide this kind of thrills and chills.

Next, why is Gallup still using a registered voter survey?  That’s a weak sample type in presidential election years, where turnout gets to about 60% in a good cycle.  It’s even less informative in midterms.  Ninety percent of Democrats support Democrats in this election, but how many are likely to vote?  Independents favor the GOP by ten, but how many of them are likely to show up at a voting booth on November 2nd, and which independents are most likely to show up?

With seven weeks to go before the election, those are the answers needed to build a turnout model for a likely voter screen.  Gallup seems disinterested in doing so, though, while their competitors have all shifted to likely-voter screens and turnout models.

Gallup did find increased enthusiasm among Democratic voters this week, but that still leaves them 18 points behind the GOP.  Yet, even with that narrowing from the 23-point gap in the last three surveys, Gallup still shows the GOP adding five points to the topline gap.  In other words, Gallup is a mess.