Massie's primary is the most expensive in history. Pro-Israel groups have played a huge part.

The pro-Israel lobby that's pumped millions into Democratic primaries this year is facing the next test of its political power on the right in ruby-red Kentucky.

The American Israel Public Affairs Committee and other pro-Israel interest groups have uncorked over $9 million in a bid to unseat Republican Rep. Thomas Massie on Tuesday in a competitive primary that has shattered spending records. Prominent pro-Israel GOP donors have funneled millions more into a super PAC stood up by President Donald Trump's political operation that has spent nearly $7 million on the race. Overall ad spending has topped $32 million, making it the most expensive House primary on record, per tracking firm AdImpact.