The secretary of state shall pass upon each petition, and if he finds it insufficient, he shall notify the “committee for the petitioners” and allow twenty days for correction or amendment. All decisions of the secretary of state in regard to any such petition shall be subject to review by the supreme court. But if the sufficiency of such petition is being reviewed at the time the ballot is prepared, the secretary of state shall place the measure on the ballot and no subsequent decision shall invalidate such measure if it is at such election approved by a majority of the votes cast thereon. If proceedings are brought against any petition upon any ground, the burden of proof shall be upon the party attacking it.