By Bruce Levine–

MESA, Ariz. (CBS) — Cubs owner Tom Ricketts on Wednesday responded to a threat from Republican presidential candidate Donald Trump, who earlier in the week in a tweet said the Ricketts family “better be careful, they have a lot to hide.” Trump insinuated the Ricketts family was “secretly” spending money against him.

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“It’s a little surreal when Donald Trump threatens your mom,” Ricketts said. “The fact is whether it’s my mom or my dad on his Ending Spending stuff or my sister on marriage equality issues or my brothers and what they do or what we do with the team, we are pretty much are an open book. We stand up for what we believe in. We support the causes we think are important. That is what America should be. That is who we are.”

Ricketts’ father, Joe, is the founder of Ameritrade and patron of the family fortune, but he doesn’t have any active role in the baseball club. Joe Ricketts is active politically, spending his wealth on efforts to curtail government spending.

There’s little secrecy surrounding the Ricketts’ spending against Trump. This January, Joe Ricketts’ wife, Marlene, contributed $3 million to the anti-Trump Our Principles political action committee, according to federal election campaign reports.

The group paid for anti-Trump ads and mailers before the Iowa caucuses and the New Hampshire and South Carolina primaries, according to the campaign reports.

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Joe and his son, Todd, lead the Ending Spending super-PAC.

“If we had something to hide, you people would have found it by now,” Tom Ricketts said. “I have no idea (what Trump was warning of).”

For his part, Ricketts is focused on baseball, not political drama.

“My job is executing a plan to win the World Series,” Ricketts said. “What other people in my family do is their day job. I support everything they do. It’s just not my focus. Once again, the stuff that happens on the political side is not my daily focus.”

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Bruce Levine covers the Cubs and White Sox for 670 The Score and CBSChicago.com. Follow him on Twitter @MLBBruceLevine.