In his first visit overseas as US secretary of state, Marco Rubio is seeking to send a message. Mr Rubio is travelling to Panama, Guatemala, El Salvador, Costa Rica and the Dominican Republic this week. "Part of this trip is about countering China," his spokesperson Tammy Bruce told Fox Business. It's an overt admission, and something that is usually thinly papered over with more diplomatic language about strengthening ties. But China's economic influence has steadily grown in resource-rich Latin America over the past two decades, and it is a cause for concern for the new Trump administration. So what does…