Question: Who was the Republican Senator of Mississippi that has been in office since 2007, who in 2013 was a letter addressed to that contained ricin?

Context paragraphs:
April 2013 ricin letters: On April 15, 2013, an envelope that preliminarily tested positive for ricin, a highly toxic protein, was intercepted at the US Capitol's off-site mail facility in Washington, D.C. According to reports, the envelope was addressed to the office of Mississippi Republican Senator Roger Wicker.  On April 17, 2013, an envelope addressed to President of the United States Barack Obama preliminarily tested positive for ricin.

Pastoral letter: A pastoral letter, often called simply a pastoral, is an open letter addressed by a bishop to the clergy or laity of a diocese or to both, containing general admonition, instruction or consolation, or directions for behaviour in particular circumstances.  In the Catholic Church, such letters are also sent out regularly at particular ecclesiastical seasons, particularly at the beginning of fasts.  In most episcopal church bodies, clerics are often required to read out pastoral letters of superior bishops to their congregations.

Yser Testament: The Yser Testament (Dutch: "IJzertestament" ), officially the Open Letter to the King of Belgium Albert I (Dutch: "Open brief aan den Koning van België Albert I" ) , was an 11-page open letter addressed to King Albert I and published on 11 July 1917 during World War I.  The letter's author, the philologist Adiel Debeuckelaere, set out a number of grievances relating to the treatment of the Flemish within the Belgian Army fighting on the Yser Front during World War I, especially concerning the perceived inequality of French and Dutch languages.  It demanded that new legislation to equalise the status of the two languages be introduced after the war.  The letter was the most famous action of the Frontbeweging and is considered an important moment in the history of the Flemish Movement.

List of United States Senators from Utah: Utah was admitted to the Union on January 4, 1896, and elects senators to Class 1 and Class 3.  Its current senators are Republicans Mike Lee and Orrin Hatch.  In office since 1977, Hatch is currently the longest-serving Senator in Utah history, the longest-serving Republican Senator and the second most senior Senator overall, after Vermont's Patrick Leahy.  Senator Hatch has also been the President pro tempore of the United States Senate since 2015.

De litteris colendis: The "Epistola de litteris colendis" is a well-known letter addressed by Emperor Charlemagne to Abbot Baugulf of Fulda, probably written sometimes in late 780s to 800s (decade), although the exact date is still debatable.  The letter is a very important witness to the Carolingian educational reforms during the Carolingian Renaissance from late 8th century to 9th century.  The letter shows Emperor Charlemagne's interest in promoting learning and education within his empire.

Roger Wicker: Roger Frederick Wicker (born July 5, 1951) is an American politician and member of the Republican Party who serves as the junior United States Senator from Mississippi, in office since 2007.

Circular letter of credit: A circular letter of credit was a letter of credit issued by a bank or related financial institution to a private person, usually an individual of means, which enabled that person to draw funds from correspondent banks while traveling.  This was considered safer than carrying large sums of cash.  Such letters were often issued on special paper with formal lettering and designs to discourage counterfeiting.  The circular letter of credit generally consisted of two or three separate items.  The first being the actual letter addressed to correspondent banks stating the amount of funds that can be drawn.  The reverse of the letter usually contained space to record the drawing of funds against the letter and the current balance.  The second item was a list of correspondent banks in the area where the letter holder expected to be traveling.  And the third was a signature card which was expected to be presented for comparison when drawing funds.  Banks typically charged around 1% of the value of the letter for its issuance.  Circular letters of credit were in many ways similar to circular notes which were in turn a precursor to later traveler's cheques.  Because of the expense involved, most financial institutions had minimum values for which they would issue such letters.  In the 19th century in the United States this was typically $500.  With the advent of modern electronic banking and ATMs circular letters of credit have largely fallen into disuse.

To the Youth in Western Countries: On 29 November 2015, Ali Khamenei, the Supreme Leader of Iran, published an open letter addressed to the youth in western countries.  It is the second letter of its kind, the first one having been published in January 2015.  Both were distributed via his accounts on various social media, including Twitter, Facebook and Instagram, using the hashtag #CommonWorry.  The second letter deals with Khamenei's views on the causes of recent terrorism.  It was written in response to the November 2015 Paris attacks and other contemporary terrorist actions, such as the Metrojet Flight 9268 crash and the 2015 Beirut bombings.  As of January 14, the letter has been translated to 58 languages in a collaborative effort conducted by The Representative of the Supreme Leader in the University of Mohaghegh Ardabili, Al-Mustafa International University graduates, the Ministry of Foreign Affairs, the IRIB World Service and the countries' respective embassies.

2003 ricin letters: The 2003 ricin letters refer to two ricin-laden letters found on two separate occasions between October and November 2003.  One letter was mailed to the White House and intercepted at a processing facility; another was discovered with no address in South Carolina.  A February 2004 ricin incident at the Dirksen Senate Office Building was initially connected to the 2003 letters as well.

The Poor-Whores Petition: The Whores' Petition (also known as The Poor Whores' Petition) was a satirical letter addressed from brothel owners and prostitutes affected by the Bawdy House Riots of 1668, to Lady Castlemaine, lover of King Charles II of England.  It requested that she come to the aid of her "sisters" and pay for the rebuilding of their property and livelihoods.  Addressed from madams such as Damaris Page and Elizabeth Cresswell, it sought to mock the perceived extravagance and licentiousness of Castlemaine and the royal court.

Supporting paragraphs: April 2013 ricin letters Roger Wicker
Answer: Roger Wicker