The Liberal Democrats have blamed tactical voting after slumping to sixth place in the Newark by-election.
Cabinet minister Danny Alexander said it was a "very disappointing" result but suggested some supporters had voted for other parties to stop UKIP winning.
The party has got less than 5% of the vote in nine by-elections since 2010.
Mr Alexander said it was hard for a party in power but its victory in Eastleigh last year proved the Lib Dems could win "where we are strong".
However, one Lib Dem MP said he was "baffled" by his party's efforts in Newark and called for a review of its campaign strategy.
The Lib Dems got just over 1,000 votes in Newark, trailing behind the Green Party and an independent candidate, as well as UKIP and Labour, as the Conservatives held onto the seat.
It was the latest in a string of electoral setbacks for the party, which has seen it reduced to just one seat in the European Parliament and also lose representation on councils across England.
The party's share of the vote in Newark, at 2.59%, was one of its lowest in a by-election since 1945 while its vote share was 17% lower than in the 2010 general election.
Mr Alexander, the Chief Secretary to the Treasury, said this could be partly be explained by people who might have normally voted Lib Dem turning to other parties to stop UKIP getting their first MP.
"Clearly this is a very disappointing result for the Liberal Democrats but it's also clear that an awful lot of our supporters in this by-election voted tactically," he said.
"People absolutely didn't want to be represented by UKIP in the House of Commons. I completely understand that."
The Lib Dems have performed poorly in by-elections since they entered government in 2010, although they did retain Eastleigh, the one seat they have defended during that time.
Mr Alexander said that victory showed "in areas where we are strong, where we have parliamentary and local authority strength, we continue to do well in those elections".
But John Pugh, Lib Dem MP for Southport, said he had tried to offer his help in the run up to the Newark vote, but found that there was no campaign headquarters in the constituency.
He told the BBC that he then received an email in the last few days before polling day, but that the party "didn't try very hard".
The party's campaigns department, he added, must have a "review of its strategy" if the party was to "recover from a roll of poor results".
In a council by-election earlier this year in Newark, the Lib Dems received fewer votes than a candidate representing the Bus Pass Elvis Party.
Nick Clegg's party avoided that fate in Thursday's by-election, with the Bus Pass Elvis party coming ninth but they were only one place ahead of the Loony party.
Referring to that moment, the former MP Lembit Opik joked about the party's performance in Newark.
"So, Lib Dems come 6th in Newark by-election, behind Independent & Green, but AHEAD of Nick The Flying Brick (Loony). The revival has begun," he wrote on Twitter.
He added: "Nick The Flying Brick (Loony) may dismiss poor result, behind even LDs, as he's never done well in Newark; but I call for Nick's resignation."