I agree. It's no secret that a much of Trump's support comes from liberals and those all-important independents that Romney worked so hard to attract.
It's not "scary," though. Of course those liberals who support Trump will naturally seek a liberal candidate. An earlier article quoted a New Yorker who spoke to liberal friends who support Trump. They were convinced Trump had changed his positions for the election only and actually still held the liberal POV.
So if Cruz were to start attracting liberal voters, we should just shoo them away and lose their votes. Such a ‘winning’ genereal-election strategy.