OTTAWA -- The approach of the final fortnight of federal electioneering before the Oct. 19 vote has Canada's political combatants fine tuning their advertising campaigns.

Conservative Leader Stephen Harper took time off from the election trail Wednesday to cut some new ads, the New Democrats have rolled out hard-hitting radio spots targeting Liberal Leader Justin Trudeau, and the Greens are finally getting into the paid media game with new 30-second TV ads they say will run on the major networks.

Only the Liberals appear to be holding pat.

Pollster Greg Lyle of Innovative Research Group, which does independent, non-partisan opinion research, says the two major English-language Liberal ads already airing are among the best he's tested with focus groups, which might explain why the party isn't rushing to adjust the message.

"The Liberals looked like a dead man walking at the start of this campaign," said Lyle. "It looked like the NDP was going to rip the heart out of them, and it didn't happen."

With the approach of the Thanksgiving long weekend, when families gather and political opinions get shared, roasted and consumed along with the autumn harvest, the political pitches will intensify.

Jason Lietaer, a Conservative strategist who is not working on the current campaign, said party advertising in the home stretch has two purposes.

"Highlight a big issue that you want people to pay attention to -- a key difference between you and the other folks," said Lietaer. "And, secondly, frame the ballot question in a way that forces people to make the choice you're looking to have them make."

"The best ads can do both of those things simultaneously."

Here's a look at the campaign air wars so far:

Conservatives:

Innovative Research has been testing the impact of party ads for several months and found the first iteration of the Conservative "interview" ad, in which a group of prospective employers label Trudeau "just not ready," were highly effective.

Lyle said Conservative party support has been suppressed by what he calls "circumstances and bad luck" but those issues -- the Duffy trial, the tragic story of an extended Syrian family wanting to come to Canada, a candidate videotaped peeing in a cup -- are now behind the party.

He's curious to see the next round of Conservative ads.

His focus group testing found that viewers tend to tune out or discount ads they feel they've already seen, which dampened the impact of the multiple versions of the interview ad. A series of ads in which Harper speaks about different issues to a round table of prospective voters may suffer from the same problem.

"They keep doing this thing where they come up with a single look and feel and then do several executions of it. I don't think that's working for them," said Lyle.

Still, the original "just not ready" ad was devastating. It's still airing, now with a red banner across the bottom of the TV screen trumpeting the core message.

For Trudeau, said Lyle, "the one thing he couldn't change in August was that he wasn't moving perceptions of competence -- which is, of course, what the Tories were focused on."

Liberals:

The two main English-language ads airing on paid media have been highly effective in focus group testing, said Lyle, even though the ads both break traditional ad-making rules.

The first ad had Trudeau directly repeating and challenging the "just not ready" label -- a no-no in political ads, where you never repeat your adversary's slur.

Yet Lyle's focus group work found the Trudeau counter-challenge was able to influence both Conservative-leaning and NDP-leaning voters.

The Liberals' subsequent escalator ad, in which Trudeau appears to be standing still as he walks up a down escalator, also worked "very, very well" in focus groups, said Lyle, but had more impact on Tory-leaning viewers.

"The escalator ad wasn't supposed to work with the sound off," said the pollster. "Well, it turns out that people watch TV with the sound on. Go figure. And it's worked."

New Democrats:

Lyle said the NDP ad that tested best, so far, was a spot that aired before the election campaign began in which Mulcair ends up speaking directly to viewers from a table in a coffee shop.

This week, amid sagging poll numbers, the NDP has released three new radio ads that directly attack Trudeau for specific actions, including his acceptance of speaking fees from charitable groups while he was an MP and his support of Conservative anti-terror legislation.

Innovative Research has not yet run those ads past focus groups.

"The question in my mind is, will people think they're credible?" said Lyle.

Viewers always say they dislike negative ads, but the ads do have influence, he said.

"If (listeners) think this is a credible ad with relevant, interesting information -- but they don't like the tone -- it doesn't matter. That ad can work like a charm."

Green party:

For the first time this campaign, the Greens will begin airing TV spots this week on the major networks.

The two paid media ads feature accolades for Leader Elizabeth May, who appears with other Green candidates, while a second, 30-second spot features former CBC weather forecaster and Green candidate Claire Martin talking about the democratic deficit.

What to watch for:

Lyle says its a bit of a myth that there's a huge pool of truly undecided voters out there at this point in the campaign. Most undecideds will end up voting the way they've always been leaning.

The pollster puts the proportion of really unattached, persuadable or conflicted and information-seeking voters between 15 and 20 per cent.

Those are the votes truly open to persuasion, at least in English Canada. (Quebec, he notes, is far more volatile.)

Based on advertising so far, here's Lyle's assessment of the main party pitches:

"You can see Harper's message: Who's best to protect Canada from fill-in-the-blank? You need a strong leader."

Trudeau's message has urgency, said Lyle: "There's big stuff that needs fixing and I'm going to do it right away. If you want dramatic change right now, vote for me."

Mulcair's message is that change is needed, but that it must be done carefully: "He's Stephen Harper, but with a heart."

"To many degrees," said Lyle, "the Tories and NDP are framing a similar question, which is the need for strong, stable leadership."