Justin Trudeau's star is slipping and Thomas Mulcair is faring no better, but the Conservatives have been unable to sway more voters to look their way, a new poll suggests.

While the Liberals are still ahead in public support, results of a rolling poll by Nanos Research suggest a declining number of Canadians would consider voting for either Mr. Trudeau's Liberals or Mr. Mulcair's New Democrats.

And an increasing numbers of respondents say they would not consider voting Liberal or NDP – or Green, for that matter.

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The Conservatives, meanwhile, started off behind the Liberals and the New Democrats in terms of being an option for voters – and they are still behind. But they are holding their own.

"There's been speculation on the Justin Trudeau honeymoon. And I think it would be fair to say that, in June, it was a honeymoon because the percentage of Canadians that would consider voting Liberal was actually exceptionally high," Nik Nanos, the president of Nanos Research, said. "But we've seen a drop in what I will call the accessible pool of voters for the Grits even though their support has remained relatively stable," he said. The same is true of the New Democrats, he added.

When the polling company asked 1,000 randomly selected Canadians in June whether they would consider voting for the Liberals, 62 per cent said yes while 26 per cent said no.

When respondents were asked the same question between Aug. 25 and Sept. 21, the proportion of people who said they would consider voting Liberal was down to 51 per cent while the number of those who would not consider voting Liberal was up to 38 per cent. The numbers for the NDP, meanwhile, took the same trajectory. Between June and September, the proportion of people who said they would consider voting NDP fell to 43 per cent from 58 per cent while the number of people who would not consider voting NDP climbed to 44 per cent from 30 per cent .

Over the same period, the number of voters accessible to the Conservatives changed only slightly and within the margin of error. The proportion of people who said they would consider voting for the Tories dipped slightly to 40 per cent from 42 per cent, while the number of people who said they would not consider voting for them fell to 49 per cent from 52 per cent.

The Green Party started off behind all the parties and, by September, just 24 per cent of respondents said they would consider voting Green while 63 per cent said they would not.

"It's almost like a pox on the opposition parties," said Mr. Nanos. "All three of the (national) opposition parties are down, only the Conservatives remain steady."

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Nanos recruited the poll participants by telephone and then asked them to complete a survey online. A sample of 1,000 national respondents is expected to accurately reflect the opinions of the broad Canadian public within 3.1 percentage points 19 times out of 20.

The good news for the Liberals is that the overall support for the various political parties has not changed dramatically, said Mr. Nanos.

The new poll did not include those numbers but, in a survey released by Nanos earlier this month, the Liberals had the support of 35.7 per cent of decided voters, the Conservatives were at 29.5 per cent the NDP was at 24.8 per cent, the Greens were at 5.5 per cent.

In June, when the number of respondents who said they would consider voting for an opposition party was higher, a spending scandal in the Senate was causing headaches for the Conservatives. The government's decision to prorogue Parliament, which has prevented the opposition from asking questions of Prime Minister Stephen Harper and his ministers in the House of Commons, had reduced what was a daily stream of negative press.

Although there has been a shift in voting consideration, the opposition parties don't have to worry because their potential is still good, said Mr. Nanos.

"What this does show is that there is not the same sort of excitement about the opposition parties today as there was in June," said Mr. Nanos. "I think this is more likely the new normal."