Cast Generic<Derived> to Generic<Base>

I have a base WPF UserControl that handles some common functionality for derived UserControls. In the code-behind of any derived UserControl I call an event

private void SomeClick(object sender, RoutedEventArgs e) {
    HandleClick(sender);
    MyDataGrid.Items.Refresh();
}

In my base UserControl I do

public class BaseUserControl : UserControl {
   protected void HandleClick(object sender) {
       var vm = (BaseViewModel<Part>)DataContext;
       ...
   }
}

This throws an since DataContext is of type BaseViewModel but of a derived type like BaseViewModel<Wire> or BaseViewModel<Connector>.

How can I cast that?