What veteran consultants and party professionals — on both sides — agree on is that the landscape has shifted — subtly but still shifted — toward Democrats in the past few weeks. It’s movement that has been most well documented on the presidential level but, in conversations with people paying close attention to Senate and House races, is also happening downballot...

...Among the reasons proposed to us by Republicans:

* The Democratic convention bounce has lingered well into September, with the framing that former President Clinton put on the race in his convention speech working against the GOP. Clinton, in a way Obama has not/can not, was able to set the stakes of the election and the choice before voters — particularly wavering Democrats — in a powerful and very high-profile speech that continues to resonate.

* There’s been a jolt of optimism in the country of late, most markedly in an improving “right track” number in most state and national polls. While more people still say the country is headed in the wrong direction, the differential is not so lopsided as it’s been in past months. Moving hand in hand with that increased optimism is the number of people who say they approve of Obama’s performance on the economy.

* Former Massachusetts governor Mitt Romney’s campaign has struggled to push its preferred message — Obama is mishandling the economy and it’s time for a change — for at least the last two weeks. “When was last time Obama was on defense?,” asked one experienced GOP strategist closely monitoring downballot contests. “The ‘it’s not about me, it’s about you’ strategy only works if your opponent is continually taking on water and you’re not.”