Fears that a high abstention rate could help far-right candidate Marine Le Pen in France's presidential runoff strengthened on Tuesday when two-thirds of far-left supporters said they intend to abstain or cast a blank ballot. An internal survey of supporters of defeated far-left firebrand Jean-Luc Melenchon showed only 35% would back pro-EU centrist Emmanuel Macron, Le Pen's rival and the frontrunner.