To a large extent, these poll numbers, as reported by Gallup, are the result of stumbles by President Obama; to some extent, they're the result of the impression that Obama is stumbling even when he isn't. But beyond that is the fact that the Republican Party has been on (somewhat) better behavior lately, and the (slight) improvements seem to be enough for the public:
Americans' views of the Democratic and Republican parties are now similar, mainly because of their more positive ratings of the GOP. Since bottoming out at 28% last fall during the government shutdown, Americans' opinions of the Republican Party have grown more positive and are nearly back to pre-shutdown levels....The folks in the GOP establishment -- the Chamber of Commerce, Karl Rove, Reince Priebus -- have labored mightily to suppress obvious manifestations of the tea party's sociopathy. This image-repair program has largely succeeded: Republican candidates exhibiting florid racism, homophobia, sexism, conspiratorialism, and so on may still be showing up in local races, but wild-card candidates have failed in high-profile races such as the Senate primary contests in Georgia, Alaska, and Kentucky. So Todd Akins and Christine O'Donnells aren't embarrassing the party as they have in the past. In addition, no one's tried to shut down the government or put the country into default for, oh, nearly a year now. Give them all an A for Conduct.
Americans have typically rated the Democratic Party more positively than the Republican Party since the question was first asked in 1992, so the current parity between the two is a positive sign for the GOP and a negative one for the Democratic Party....
But this just reminds us how little Republicans actually have to do to be deemed sane and rational. They're still blocking the president's entire domestic agenda. They're attacking him during what they regard as a foreign policy crisis in a way that they would have called treasonous if the parties were reversed. They're still trying to repeal Obamacare. They're still investigating Benghazi. They're still threatening future shutdowns, and possibly even impeachment.
We don't expect much of the GOP. It's fine if they refuse to allow the country to be governed just so long as they don't actively trash the place, and boast about doing so. They know that. So they've done all the rebranding they need to do.
The tea party now just acts as the bad cop, thus allowing the slightly-less-bad manistream GOP cop to seem good. They're both roughing us up. But the "good" cop is getting away with it.