They make some valid points, and I mostly agree with their characterization of the media, but overall I think it's misguided to think that the country is being overrun by right-wingers. The balance of power has certainly shifted to the right for the time being, and they're trying to take maximum advantage of it, but I think it's just one in a series of shifts, and it will probably shift again as people get tired of right-wing rhetoric and hypocrisy, just as they sometimes get tired of left-wing rhetoric and hypocrisy. Over time, worthy ideas are taken from both the right and the left, but moderation usually wins out (actually, in the long run, liberal ideas usually win out over conservative ones - see below). We can already see that although most of the country bought into the Bush administration's war rhetoric, the balance has swung against it. Some of this is due to fatigue, but some is due to the realization that a lot of the rhetoric was hollow and that the administration has some serious competency problems. The same goes for the anti-gay stuff - the Republican Party feeds rhetorical anti-gay red meat to its hard-core base, but in the end most Americans will tire of it and realize that we have more important things to worry about. That's one reason the Republicans lost the Soccer Moms in 1992 and 1996 and could lose them again this year. Don't forget that even clumsy old Al Gore got most of the popular vote in 2000.
The same thing happens when things swing too far to the left. Many important liberal values of the 60s and 70s became part of the mainstream, but they also became corrupted in some ways, resulting in various swings back to the right.
Bear in mind that although Republicans have been winning at many of the polls, overall this country is a far more liberal place than it was 40 years ago. Even conservatives take certain liberal values for granted that they would have vigorously opposed before. As Peggy Noonan has said, liberal Democrats are, in a sense, victims of their own success - conservative Republicans have adopted so many liberal values over time that Democrats have trouble finding ways to get voters energized. Republicans, of course, always seem to manage to find ways to piss people off, giving the Democrats another chance.
This time the Republicans run the risk of pissing off the center with anti-gay rhetoric and misleading war rhetoric. I suspect that the anti-gay issue will fizzle out as most sensible people lose interest (another liberal victory), but if the Republicans put too much emphasis on it, it may well backfire on them. More likely, the election will turn on how things are going in Iraq. If it's still a violent muddle, I think most people will say "OK, Bush gets credit for making a tough decision, but he didn't execute it very well, and I'm tired of the good-ol'-boy act, so let's get someone in there who's a little more sophisticated." If things go better in Iraq, his odds improve, although I suspect that a lot of people will still conclude that they'd like to have a President who's more engaged intellectually and isn't pandering to the Religious Right (which is pretty much what happened in '92).
I think that after people get tired of the gay rights issue, the big battleground will be health care. The Clintons were premature and handled the issue poorly, but I think the political will to make serious changes is growing. Whether it will happen soon enough to help Kerry remains to be seen, but I think it will happen eventually.
These authors describe themselves as progressives, and the fact is that progressives will never be completely happy with things, no more than the Religious Right will ever be completely happy. Things shift left or right but pretty much always rotate around the center, which makes both of those contingents cranky no matter what.