Attacks on Ted Cruz’s eligibility for the presidency have seriously undermined his campaign in the crucial days before the Feb. 1 caucuses in Iowa.

Today, we describe that eligibility as an open question that cannot be resolved easily, in part because the Cruz campaign is withholding the facts about his birth in Canada that are necessary for clear-cut resolution.

We explore also recent revelations that the first term Texas senator won his upset victory in his 2012 campaign with the help of $1.2 million in Goldman Sachs and Citigroup loans that he failed to report as required by federal election law.

Both issues are important because they coincided — and probably helped cause — Cruz’s decline in the Iowa polls over the past month. Donald Trump now leads in the most recent Iowa poll, as of Jan. 30, by a 5 point margin, according to the prestigious Des Moines Register poll conducted with Bloomberg News.

Trump held a 6.3 margin over Cruz in a RealClear Politics average of six recent polls, as of Jan. 30. Cruz had led or tied in four straight Iowa polls between Dec. 17 and Jan. 7, according to the RealClearPolitics summary.

But on Jan. 5, GOP rival Donald Trump used a New York Times interview to question Cruz’s eligibility for office under the U.S. Constitution’s requirement that a president must be a “natural born” citizen. The Founders did not define the term in the Constitution. But it was widely understood at the time of the Revolution to require birth on a nation’s own territory for the most part.

In crafty fashion, Trump (shown in a file photo by Gage Skidmore) did not raise the question as an outright attack on Cruz, but floated it in response to a reporter’s question more as a concern that Democrats would litigate the issue for years, thereby damaging the Republican Party and the nation.

Whatever Trump’s intention, he has since moved more into outright attack mode on the question and prompted a massive pro-and-con constitutional debate among legal scholars and pundits. The leading arguments are excerpted below in an appendix, enabling anyone to form at least a preliminary judgment.

Shortly afterward came the revelation of Cruz’s unreported campaign loans from two top Wall Street investment banks. Most came from Goldman Sachs, which employs Cruz’s wife Heidi Cruz as a managing director in its Houston office.

Cruz dismisses both matters as non-issues, as described more fully below.

But each accusation put his campaign on the defensive, particularly they both undercut his campaign image. For one thing, he opposes leniency in immigration law and favors “strict construction” of the Founders’ language in the constitution. Additionally, Cruz memorably opposed “New York values” supposedly embodied by Trump – but surely also by the top financial institutions that control so many leaders in Congress and the Executive Branch via lavish donations and other payments to officeholders.

The Goldman Sachs taint became especially newsworthy this month because federal authorities imposed $5.1 billion in fines and other penalties on Goldman Sachs for its actions helping cause the 2008 financial crisis that so deeply hurt so many Americans.

The senator, a star student at Harvard Law School and former Texas solicitor general, has dismissed the loans as a bureaucratic oversight of scant importance. He thereby suggests what his fans regard as commendable anti-regulatory focus – and what opponents regard as additional reason for deep suspicion and scrutiny.