Should the Conservatives lose their two parliamentary seats in Kingswood and Wellingborough, the party will exceed its record of by-election defeats in a single parliament.
There is a chance too that the party could experience its worst ever defeat to Labour, on course to capture both seats.
But emerging divisions within Labour, over the conflict in the Middle East and now the ditching of the green investment pledge, could check its electoral progress.
The Conservative battle with Labour may ease, but the party is still threatened by strengthening support for Reform UK.
It is contesting both vacancies and targeting votes from disillusioned Conservatives.
Should that happen, then more Conservative incumbents facing boundary changes in their current constituencies, may feel the easier option is flight not fight.
By-elections in this parliament started so well for the Conservatives. In May 2021, it gained Hartlepool from Labour, one of the very few occasions when a party in government has captured a seat off the opposition.
Tory euphoria evaporated when, barely a month later, the Liberal Democrats seized the safe Conservative seat of Chesham and Amersham.
Worse followed. The resignation of sitting MP Owen Paterson, guardian of the rock-solid North Shropshire constituency, preceded a memorable Conservative defeat. A 23,000-vote majority vanished with a near record 34-point swing against the Conservatives.
Since then, a further six Conservative by-election defeats. Two more defeats to the Liberal Democrats but, ominously, four to Labour and with big swings in the bargain. A net loss of seven seats and counting for the Conservatives.
This situation brings comparisons with the 1992-1997 parliament, as John Major led the Conservatives to one of its worst general election defeats in 1997.
During those five years, the Conservatives lost eight by-elections - four to the Liberal Democrats, three to Labour and one to the SNP.
The contest in Wellingborough is because Peter Bone, first elected in 2005, was found guilty of inappropriate behaviour towards a staff member, suspended from the House of Commons and forced to resign following a recall petition signed by his constituency's electors.
Bone, a prominent member of the Vote Leave campaign, had built the Conservative majority to 18,540 votes and a 36-point lead over Labour.
The required 18-point swing should be within Labour's reach, assuming that its supporters are not deterred by emerging disagreements within the party.
But Wellingborough will certainly grab our attention if the Conservative vote is eroded by Reform UK, whose candidate, Ben Habib, is its co-deputy leader.
At the last general election, Reform's predecessor, the Brexit party, gave over three hundred Conservative MPs a clear run to victory.
Not so this time, it appears, and with Reform currently polling close to 10% in national surveys, a large bloc of disaffected Conservatives moving in that direction significantly changes the electoral arithmetic.
A lot depends on turnout. Last October, the Conservatives lost Tamworth to Labour, but just 35.9% of the electorate voted, setting a record for the lowest turnout since 1945 where the seat changed hands.
We don't know for sure whether this only happened because Conservative supporters preferred to stay at home, but it has to form part of the explanation.
Electoral indifference has been a feature of by-elections this parliament, an average 29-point drop in turnout compared with the previous general election.
Should Wellingborough break that trend (64% turnout in 2019), it may be that Conservatives, instead of abstaining, have chosen to support Reform in a constituency where 63% voted in 2016 to leave the EU.
Kingswood is the more vulnerable seat for the Conservatives, a by-election caused not by an MP's recalcitrance but rather disagreement with his own party. Chris Skidmore, a former Cabinet Minister for Energy, resigned over the government's plan to issue more licences for oil and gas extraction.
In what had been a Labour seat, Skidmore successfully increased his majority over Labour from 5.1% in 2010 to 22.8% last time. By contrast, Labour's vote share fell in three of the last four general elections.
But an 11.4-point swing is all that Labour's Damien Egan requires, smaller than that implied by national polls.
A measure of confidence is that Egan resigned from being Mayor of Lewisham to fight a vacancy in a constituency that, because of boundary changes, disappears in a matter of months.
His actions become clearer when we learn that he had already been selected for the new Bristol North East parliamentary seat, where estimates are that Labour would have won at the 2019 election.
As before, Reform are fielding a candidate where UKIP polled 15% in the 2015 election, finishing in third place and ahead of the Liberal Democrats suffering a post-coalition government hangover.
It was during that coalition, specifically 2010-2012, that the party's leader, Sir Ed Davey, had ministerial responsibility for the Post Office. Davey's initial failure as minister to meet with campaigner Alan Bates has seen his name drawn into the wider scandal.
National polls suggest Reform and the Liberal Democrats have similar levels of national support and they could be competing for third place in Kingswoood. There's a further twist to this battle, with the two remaining candidates representing the Greens and UKIP respectively.
Now that Labour has abandoned its £28bn spending pledge on environmental issues the green vote, consistently around 2% in this constituency, might be boosted by Labour defections as well as Liberal Democrats disappointed by the party leader's association with a miscarriage of justice.
Meanwhile, UKIP's presence extends the choice for Brexit die-hards and could weaken support for Reform.
Unpicking these two by-election results, expected in the early hours of Friday, will provide important clues regarding the direction of change as the next general election moves ever closer.