Engine won't turn over, 115K miles, starting issues

2012 Ford Focus, 115 000 miles. Starting issues. A few weeks ago I would turn the key in the ignition and there would be nothing for about 3 or 4 seconds and then it would turn over. Now it does not turn over at all sometimes. Sometimes it starts right up and other times it does not. The lights on the dashboard still come on but it just does not turn over. Loose connection somewhere? Starter relay? Battery?

I would check battery cables and ground connection.