Jo Swinson slammed Boris Johnson in a Scottish campaign rally, claiming he has "never been much of a family man".
The deeply personal dig was clearly meant to highlight his private life and underlined an increasingly bitter struggle to push him out of power .
Swinson, in Edinburgh, pledged to keep Scotland in the UK , and the UK in Europe.
"Boris Johnson says he is committed to our family of nations," she said.
"But we all know that he’s never been much of a family man.
"Why else would he try to put a border down the Irish sea?"
Swinson also claimed Johnson is trying to style himself as "Britain's Donald Trump".
She later took part in a fairground-style game by throwing bean bags at soft toys depicting Johnson and Trump.
Activists lapped it up but Lib Dems have a mountain to climb in the general election
Despite stalling in the polls, insiders were briefing potential gains including in SNP Westminster leader Ian Blackford's seat.
One party official claimed one in two Tories in the Ross, Skye and Lochaber constituency were tactically voting Lib Dem.
SNP figures rejected the claim last night, insisting their vote is holding up.
