Dan Thomas made the claim after Plaid did not get through extra spending plans.
Opposition parties criticise Plaid after it announces "ethical" policy for backing defence companies.
Rhun ap Iorwerth says the process of talking to opposition has started in a bid to avoid a second defeat.
The announcement came as the prime minister makes first official visit to Wales since taking office.
The new Welsh government elected in May is likely to face more intense scrutiny in the coming months.
Wales political editor Gareth Lewis looks back on Plaid's first 100 days in power.
Plaid ministers say they are making good progress but the opposition say little has been achieved.
In an era when reputations can be made or broken with a single post, getting the balance right is tricky.
Six blazes burn as major incident continues in south Wales, but military due to be withdrawn.
