Are there limits on foreign fund raising?

I see Rudy Giuliani is in London to raise money, and apparently he wasn’t the only candidate.
Can a Saudi prince or a foreign government, say North Korea, try to buy an election by simply handing someone a billion for blanket coverage TV ads?
Are there limits of any kind?

There are laws against aliens who are not permanent residents making contributions to political campaigns in the US, but I don’t know the details. But perhaps Rudy was addressing his appeal to US citizens living in the UK.

Foreign nationals may not make contributions in connection with any election–Federal, State or local. Per the Federal Election Commission

On the NBC national news last night, they did mention the rationale behind the trips was because there were so many Americans living abroad now.

Yes there is a limit: $0.

The people who contributed were US Citizens. Any non-US citizens who were they may have been admitted gratis or with a contribution to charity. But Rusy couldn’t accept anything from them.

US candidates follow money trail to London