By telling Ukraine the conditional (A ⇒ B)

"If you join our alliance, we will defend you from an attack."

NATO was not quite telling Ukraine (¬A ⇒ ¬B)

"Until you have joined our alliance, we will not defend you (from an attack)."

The only logical certainty is (¬B ⇒ ¬A)

"If we do not defend you, then you have not joined our alliance."

This distinction is small consolation for the civilians being bombarded into submission in various Ukrainian towns, or to the President and government of Ukraine who do not know whether the "diplomatic talks" are pointless because President Putin has already decided to eliminate (exile or assassinate) them.

But the statement

"If you join our alliance, we will defend you."

comes exceedingly close to telling Russia

"Ukraine is helpless until joining NATO."

or even, extrapolating

"We will not intervene to defend Ukraine from an attack until Ukraine joins NATO."

The last two statements nearly invite an attack by Russia. "It is now or never" might be what the Russians heard.

Did extended NATO membership discussions make Ukraine a sitting duck?