The 2012 law co-written by U.S. Sen. Susan Collins to prevent insider trading and bolster transparency in Congress — which has been violated by her and dozens of others — is facing scrutiny from those in both parties pushing for tougher restrictions. Polls over the last two years suggest 86% of Americans, and up to 95% of Mainers, back a ban on individual stock trading across the three branches of government. Lawmakers eager to score wins in a c…