Fewer Canadians were willing to consider voting for the NDP or the Liberals this month than in June, according to the latest Nanos Tracking Survey.

The number:

15

The percentage-point drop in potential supporters for the NDP since June.

​Source: Nanos Weekly Tracking Survey. Random telephone interviews (cell and land-lines) of 1,000 Canadians using a four week rolling average of 250 respondents each week. Conducted Aug. 25 - Sept. 21. Accurate to within 3.1% points, 19 times out of 20

Respondents were asked whether they would consider voting for each party.

In June, 62 per cent of Canadians said they would consider voting Liberal, 58 per cent said they would consider supporting the NDP, 42 per cent were open to voting Conservative and 39 per cent said they'd consider voting for the Green Party.

After the summer months, the Liberals are still in the lead but have seen their potential supporters drop 11 percentage points to 51 per cent of Canadians. Forty-three per cent said they would consider voting NDP, down 15 points.

And support for the Conservatives was basically unchanged at 40 per cent. The Green Party was also down 15 points with 24 per cent.

Federal Vote Consideration (June)

Source: National Nanos RDD Crowdsource random survey conducted June 16 - 19. Participants randomly recruited by telephone through the proprietary Nanos Crowdsource sample and administered online survey. Accurate ±3.1 percentage points, 19 times out of 20. (CBC)

Federal Vote Consideration (September)

​Source: Nanos Weekly Tracking Survey conducted Aug. 25 - Sept. 21. (CBC)

The Nanos Weekly Tracking Survey data is based on random telephone interviews, cellphone and landlines, of 1,000 Canadians using a four-week rolling average of 250 respondents each week. The latest survey was conducted between Aug. 25 and Sept. 21 and is accurate to within 3.1 percentage points, 19 times out of 20.

Nanos said these numbers might show the "shine wearing off for the opposition parties."

In the spring and into June there was a lot of excitement around the new Liberal Leader, Justin Trudeau, and for NDP Leader Tom Mulcair following his performances in the House of Commons, but that excitement has not carried through the summer months, Nanos said.

"For Stephen Harper there's no big change, he's had to deal with the controversies over the Senate, kind of try to fight his way through the summer and there's not a significant change for the Tories," Nanos said.

But while the opposition have seen a drop on this question, Nanos points out that the Liberals still have a six-point advantage over the Conservatives in the latest horse-race numbers. The NDP is still trailing.

The latest Nanos poll showed Liberal support at 36 per cent, the Conservatives at 30 per cent and the NDP at 25 per cent. Nanos Research polled 897 committed voters who were recruited by phone and administered an online survey between Aug. 18 and 22. The margin of error is 3.3 percentage points, 19 times out of 20.

"You look at those numbers, it's not too bad for the Liberals, but the ability for the Liberals to do a significant smash and grab at this point in time is diminished," Nanos said.

The Conservatives have to look at the potential support numbers and figure out what do they have to do to stop Justin Trudeau and the Liberals so they can't grab votes "that are kind of loose out there," Nanos said.

Another reason the opposition might have seen a drop in potential support is that reality might be setting in, for the Liberal leader especially.

"Which is not necessarily bad news for the Liberals, because there's still lots of potential for them. And for the Conservatives no change, they are rock solid where they are," Nanos said.

Nanos points to another factor that might affect support numbers — the interest by a handful of NDP MPs in running for the NDP leadership in British Columbia.

"It's going to be interesting to see whether the B.C. NDP leadership becomes an infomercial for the New Democrats. B.C. is a critical battleground and having some federal candidates in that leadership race could hypothetically help the New Democrats," Nanos said.

Nik Nanos digs beneath the numbers with CBC News Network's Power & Politics to get to the political, economic and social forces that shape our lives. Recognized as one of Canada's top research experts, Nanos provides numbers-driven counsel to senior executives and major organizations. He leads the analyst team at Nanos, is a Fellow of the Marketing Research and Intelligence Association and a Research Associate Professor with SUNY (Buffalo).