What a poor night it was for Stephen Harper's Conservatives. If the results of Monday's four federal by-elections didn't worry the Conservatives, nothing will.

The results collectively showed two things. First, the Conservatives are in political trouble. Second, it's the Liberals, not the New Democrats, that are the Conservatives' most formidable opponents.

In the two head-to-head Liberal-NDP races – Bourassa in Montreal and Toronto Centre – the Liberals won convincingly. They were expected to hold both seats, and they did.

Story continues below advertisement

The NDP's failure to make either riding a close contest suggests the bloom is off their rose. The Liberals are now the Conservatives' mortal threat. NDP Leader Thomas Mulcair appeared often in the two ridings, hoping for an upset. He failed, and the party failed, in both cases by wide margins.

Of course, the Conservatives will brush off their poor performance as nothing more than the uncertain tests of mid-term contests. Their spin machine went into overdrive to explain the results as nothing serious.

Yes, by-elections are not general elections. By-elections are snapshots in time that can be erased or altered in a national vote two years hence.

But Brandon-Souris? How could this riding west of Winnipeg not have been a Conservative laugher? The party lost it only once, in 1993. For the rest of the time since the Second World War, the riding was Conservative.

So weak were the Liberals in Brandon-Souris in 2011 that their candidate captured just 5 per cent of the vote. That the Liberal candidate got more than 40 per cent Monday night was an earthquake. Similarly, in the dead-safe Conservative seat of Provencher, southwest of Winnipeg, the Liberal vote soared from 8 to 30 per cent.

In Brandon-Souris, the most interesting and politically consequential of the four ridings, the Conservatives had every advantage on paper. Their candidate was a provincial MLA, well known and well liked. He had a machine, whereas the Liberal candidate did not. The Canada-European Union trade and investment deal ought to have been popular with farmers, because their exporting, especially pork, will be easier. The abolition of the gun registry and the Canadian Wheat Board were ostensibly vote-winners.

The Liberal candidate, Rolf Dinsdale, carried a famous last name, because his father Walter represented Brandon-Souris as a Progressive Conservative for three decades. But the younger Mr. Dinsdale had not lived much in the riding, nor distinguished himself in local affairs. And yet he defied all the Conservatives' paper advantages and nearly won in a riding where, normally, the only thing protecting Liberals is the game laws.

Story continues below advertisement

The Liberal showing, therefore, could not be explained by a strong local candidate or particular local issues running in the party's favour. The most plausible explanations have to be the popularity of national Liberal Leader Justin Trudeau and the dead weight of Prime Minister Stephen Harper on Conservative fortunes.

Few Conservatives will dare use the Brandon-Souris result to criticize or question Mr. Harper publicly. But a whole lot of questions have to be asked. Brandon-Souris has to be put beside last year's tight result in Calgary Centre. The Conservatives won both narrowly, but should have taken them in a walk.

The Senate scandal, where polls consistently demonstrate the public does not believe the Prime Minister, and the government's overall thuggish tone and style, are apparently eating away at the Conservatives' fortunes. Conservatives had a case to make to the voters on trade, economic management and issues such as the gun registry. They put a lot of effort and money into the Brandon-Souris. Yet the Conservatives barely won, despite having a much better-known candidate.

Only the Liberals demonstrated serious appeal in all four ridings. The Conservative totals in Bourassa and Toronto-Centre were risibly below 10 per cent, as were the NDP results in the two Manitoba ridings. The worst NDP result arguably came in Toronto Centre – a Liberal stronghold, yes, but a place where the NDP had hoped to make things close. Instead, Liberal Chrystia Freeland trounced New Democrat Linda McQuaig.

Everything the Conservatives have tried politically since the summer has failed. The Prime Minister doubled down on his narrow-casting strategy of appealing only to the party's core voters. On Monday, he paid a price.